like everyone else said, $40 is pushing it. Since you have the pc, monitor, controls, that takes some stuff out of the way, but it adds up fast.
i got an empty cabinet for $20, it came with 3 buttons, trackball, coinmechs, marquee retainer/and plexi,marquee light, monitor glass.
just look around, i did a google search for "amusements" along with the name of the town i live and i found a place locally that repairs arcade games.
but like everyone said, things add up quickly. if you have to buy wood, $40 isnt going to cut it. you won't get lowes to cut it the way you want, so you will need a saw. I dont know what kind of controller you have now, but unless you are leaving it the way it is and just sitting it on your cabinet, you will need a drill, along with a 1 1/8" drill bit.
also, you will need speakers, a marquee, marquee light, monitor glass, paint...and some misc other things you will find that you need as you go along.
as for tools, ask around, you probably know someone who would let you borrow a saw/drill/router/etc...
we are not trying to discourage you, just pointing out that all of us spent way more than what we initially planned on...thats just the way it works. as you go, you realize that there is something else you need...it just never ends.
good luck