Nice one. But don't pity me, I always know what it's really coming when asking for recommendations in such a geeky community like this. Believe me when I say I've had my fair share of flamewar, still never feel enough 
@Chimera: I do think TBO/TBE are solid products when it comes to trackballs, still I'm not going to bid over the odd for them even if I'm financial able. Let me explain why, in general I believe in "you get what you paid for" when it comes to commercial goods. A Model M which used to be priced at several hundred bucks decades ago very likely costed IBM nearly as much money to manufacture, and that amount (of money) explains its famous tank-like quality, adding inflation and it's possible to partially justifies the currently very high prices comparing to modern mechanical kbs. Antiqueness, uniqueness, nostalgia... does the rest. In short, for me a device which costed $100 to make 20 years ago, is believed to be able to serve for 50 years (with good reasons), in good condition and not an ounce of practical value lost is acceptable at $100 todays.
In case of Microsoft's trackballs, I understand they were widely available for fifty something (correct me if I'm wrong) when first released, naturally their manufacturing cost could only be as low, I believe quality and durability also went that way. By the same logic, to me they are products which costed $30 to make not a decade ago, are considered to be able to serve for much less than 50 years (again with good reasons), in good condition and not an ounce of practical value lost are only acceptable at certainly much much less than current asking prices, i.e upwards $100. Numbers may vary but my logic remains the same. Rareness, sought after-ness....makes up most of them hefty tags. Those are values I'm not ready to pay for.
From a knowledgeable consumer's viewpoint (and certainly not a fierce fan), when brandnew high-end also proved highly functional trackballs from a respectable brand like Kensington are on shelves for $75-100 with years of warranty, software support in bleeding edge OS....taking risk with discontinued, used ones in grey market for the same or higher amount is downright unreasonable.
But that's just me and my n00by opinion. Feel free to bashing me if offended.
This really doesn't apply to the TBE, you can't really base it's quality on price. I think the TBE started selling around $60-70 and eventually came down to around $40-50 before it was stopped. There are also two types of tbe's, one screw and two screws. The one screw variety are much rarer, and some believe they might be more durable, or use a different chipset in them.
Even today there are weird anomalies that are unexplained in the peripheral world, for instance the Scorpius m10 which is a 105 key blue cherry mx board, that costs half the price of a Filco with less switches, and costs way less than even raw switches cost. Weird things happen with amounts that are bought/sold, and what prices things can be made and sold at, international shipping/politics, and how much retailers want to make on the items, and how fast they want to move the stock.
They were sold for $50-60 but in this case their value is way over $150, because there's nothing that has come after them that has been an acceptable replacement. There have been acceptable replacements for model m's in over all capability. Nothing has come close to a TBE. That's why there's a huge movement to try to get Microsoft to bring them back:
http://my.galagzee.com/2007/07/03/microsoft-trackball-explorer/Anyway, these were produced in China when there probably was a much better relative exchange rate, and you have to factor in various global economic factors for the time if you really want to base quality on price. The fact that the TBE is no longer being produced to me is a sign of the fall of civilization as well. lol
The plastic quality is higher or equal to any trackball currently being produced, as well as the parts. I doubt it could be produced and sold for less than $100 if it was currently on the market.
Another factor is Kensington is a much much smaller company than Microsoft ever was, so again it's like comparing apples and oranges for price.
Besides, there's also a huge discrepancy in price that the net has created:
http://accessories.us.dell.com/sna/productdetail.aspx?sku=A0187943&dgc=SS&cid=27530&lid=627063&s=dhs$61 for a Kensington expert at dell for instance, which is $20 below the market retail value of any other store.
TBE's were marketed before the web, or at least the major impact of the web, so that also has a huge bearing on what prices and the value of them were.
The only real major durability problem the TBE suffers is the cord after many years of bending back and forth can get worn, and the outer wrapping ground wires inside the cord can break and cause intermittentcy, but it's a relatively easy fix. The chip set is rock solid and a completely failed TBE is really rare.
The ball and the carbide points have a basically infinite lifespan and or replacements, if you take care of them or where to buy them.
http://www.vxb.com/page/bearings/PROD/Kit7801 There are even ball polishers on ebay these days that will resurface a ball for like $50, for those tbe's that have been in heavy use for over 10 years. There's an entire cottage industry that has grown up for servicing TBE's, so you don't have to worry about getting minor parts, or that they're not serviced by Microsoft anymore.
TBE's are probably the only mouse or trackball to have this kind of cottage industry surrounding them to keep them going. TBE's have almost created a cult. I doubt you'd have that kind of following surrounding any other kind of mouse or trackball.
