I must agree with the statement of "why build when you can buy one for like $7?" though, there comes a point when you have to ask yourself how much your time is worth... By the time you're done constructing a working joystick you will have spent at a minimum maybe 3 hours. One might look at that as saving $7. I look at it as getting paid a little over $2/hour. It's not even a question of practicality at that point, it's simple economics.
While I can't speak directly for the OP I bet I am in a similar frame of mind as him. Many of us are here to BUILD our own arcade controls, playing with them (at least to me) is frequently secondary. I enjoy building things, much more than using them most of the time. I work in a field where we build brand new stuff from scratch so that people can look at it on a stage for about 1 month then we tear it all apart and build some new stuff, rinse and repeat. As a kid when I used to play with G.I. Joe, Matchbox, Hotwheels, Micro Machines, or whatever I always enjoyed setting up places for the play to take place and then barely doing any sort of action. Huge (well about 1"=1'-0" scale really) military bases and whole cities carved into the dirt in the backyard after hours of work, all so that when I had to go inside for the night and it rained I could do it all again the next day (rinse and repeat a little more literally this time.) Legos too, build, destroy, build again. I could never understand the kids who wanted to have battles with their G.I. Joes, or races with their cars. Even with R/C cars, I built them from the kit, charged the battery for 20 minutes, and then drove for 15 which usually resulted in breaking something which was fine because it meant I could spend the next day fixing it.
Build your joystick, hell, mine the minerals to make the metal to make the machine to turn the shaft if that's what you want to do. The process is MOST of the fun.

Of course after saying all that it dawns on me that half the time recently I can't convince myself that actually working on my cabinet would be a better use of my time than 20 more games of KLAX, WTF is wrong with me?