Yeah ebay and craigslist will be your best bet. Buy the Corneilous keg aka corny/cornie kegs, and a regulator. Some like Pin locks and while they provide a more positve lock htey are not interchangable with cornie kegs which most people have/use. Stop by a gas shop and ask for a small steel Co2 tank. 5-15lb. Don't waste your money on the Aluminum ones. With Steel you can drop off and pick up with no waiting. Fittings and keg parts can be had at most any brewshop, and kegs can be rebuilt with McMaster Carr o-rings google for the part numbers.
Last time I looked, Kegs are 30-40 each buy them one or two at a time.
My first kegerator was a converted chest cooler. You can find these for less than $100 on Craigslist, make a collar and install taps if you wish or use cobra taps to get started they are like $7 bucks. A duel gauge regulator (ebay) and braided tubing I got mine at lowes and used SS hose clamps. Pick up a temp regulator off Ebay and you are set. I find stuff on C/L all the time and bought single regulators and analog temp regulator cheap.
Some folks ferment in cornie kegs, I dont recommend it but you can. I ferment in a carboy or my Sabco then rack over to the keg w/ Co2 takes 2 minutes. I rigged a carboy cap with QD for Co2 and some copper tubing as the racking cane. VEry little pressure is required and once it starts you can increase the flow. Raise or lower the racking cane over the trub as required and turn on the gas.
If I plan my brewday correctly I will just rack my wort onto the yeast cake and hook up the blowoff tube for near instant fermentation kick-off. So I can rack off yeast cake over to keg then rack off my brew kettle through my cold plate onto yeast cake in less than 5 minutes and only clean and sanitize the keg, tubing, mash tun and keggle. No more futzing about with bottles and caps worrying about bottle bombs.
Then I apply some keg lube to the lid, lock the lid then hit w/ 18-20 lbs of Co2 rock around on the floor then stuff in my cooler to condition. Next day it is drinkable. You need to watch for carbolic acid formation but you get the idea. Most times I cold condition for months so that is not an issue. Once you get an arsenal of kegs, I have 20-5 gal ball lock and 3-3 gallon, then you can make and condition to your hearts content. Some folk lager in cornies too, you can cut your dip tube to keep from racking the trub, then rack over to another cornie using a closed system. Easy-peasy.
One can naturally ferment in a keg too, just add priming sugar then seal for that natural bubble.