If you don't mind burning through a coupla bucks just to get a feel of probably the most basic version of the switch, just simply get a used Dell AT keyboard. However, don't buy anything that says 'Dell AT101W' or something, as you want to
check with the lists of variants at Deksthority in order to make sure you aren't buying a rubber dome (FCC ID GYUR05SK, a.k.a. AT 101R, like 'R' for 'rubber') and in order to identify the odd chance you get to buy a salmon-switch Dell keyboard (FCC ID GYI3PVAT101 or FCC ID GYIAT101-102) as opposed to the usual black switch. Try to buy something that shows on the list as positively identified to have mech switches.
I bought 10 of them for $70 once, or something. They can be cheap. Obviously cheaper on office sales (like after leasing ends and/or they upgrade their stuff) than from collectors, who will want to charge a premium for the mech switch.
This said, if you come across something that has non-black alps, costs within $30 or even $40 but is in a really good condition, especially NIB or almost NIB, then you want to buy that.
Make sure you're buying the right layout unless you really really are 100% sure you don't mind. If you aren't nitpicky, you can live with minor differences in punctuation keys, so some layouts aren't as bad as some others. But you normally want the US or the UK layout unless you actually are French, German, Swedish etc. (Except for Poles, who don't use the 'Polish layout', ever, nor is it ever sold in Poland, ever).