This is a broad, difficult question to answer since most is just personal preference. You can find mechanical keyboards that start in the 50 dollar range. The ones in the 90 to 130 range may be a little better built, and you go up from there. Amazon is a good place to start and you can check out a place like mechanicalkeyboards.com.
Mechanical is not necessarily better, just different. From a strictly ergonomic view most will find them more comfortable as they actuate at about 1/2 of a keypress so you don't have to slam down your fingertips and they reduce repetitive stress.
I'll refrain from giving my opinion on what is best because it is pointless. You will want to look at switch type- tactile vs tactile with an audible click, vs linear which have no detectible actuation point and the keystroke is smoother. You can look and brands of switch- Cherry and Cherry clones (some of these less expensive clones have proven themselves and have quite a following sugh as "Gateron"), Matias switches, and then you have Topre which is a little out of the range you specified, but is built a little different. The types are sometimes labeled by color like blue, red, or brown, but these colors are not always uniform across manufacturers.
Switch weight is preference and is highly subjectible. Being a programmer I would assume you want something lighter in the 35 to 50gf range (many find 35 too light to be practible), but you also have the middle which is about 55-65gf range, and then you have the heavier ones in the 70 or greater range. These may be tiring if you spend many hours at the keyboard. As a point of reference you keyboard that came with your computer is most likely a rubber dome keyboard and may take something like 60 grams of force to actuate the key. (or a scissor switch which you see on many laptops, which has a different design)
You also have keyboard size- most programmers will want a full board, but there is also TKL or ten-key-less which are missing the numbers on the right, and there are many keyboards which are also sized about 60-70%. These smaller ones may not have dedicated keys like home and end or arrows which you probably use and are hidden behind a function layer. Strictly from ergonomics I like the smaller 60% or 70% keyboards.
All of this can be researched on this forum and you will find many knowledgeable people who are very helpful, and well sometimes very opinionated, and fun.
Alright I killed some free time, now I have some sh*# to do.
*oh, and keycap material- ABS vs PBT vs some others. ABS is generally lighter and smoother textured, while PBT is heavier and has a grittier texture. These can affect how the actual keypress feels.
