I'd try to find some used parts of you can, to keep the total price down. Here's a list of stuff I'd look for used, or new if you can't find it.
Sugino crankset 110 BDC, 48-38-28 or 46-36-26, square taper, JIS. Back in the 80's and early 90's these crank were on lots of MTBs, touring bikes, commuter bikes. Shimamo also made simular cranks (tourney) that work well. You might check out your local Goodwill or local used store for a parts bike.
The older smooth post style canti brakes are harder to set up than the new Avid Shorty cantilevers, but the old ones have about the same stopping power. The old Shimano LX cantis are great, with new pads.
Once again, look for an old MTB at Goodwill. If you're lucky, or dedicated, you should be able to score a bike with both the crank and brakes you need, as well as other spare parts.
As far as a rear derailer, think about a shiny new Deore. Shop around on line and you should find one for about $30. And new 8 speed bar-cons, for around $60. Becuase the front shifting will be friction, use any old front derailer.
There are a lot of misc. parts you going to need to finish the bike. Try to stay out of the bike shop! Something like a stem costs $30+ new. Shop around. be careful. and most of all, have fun.