you can probably fit 2 in a smaller one - the size of a standard corny keg is 8.5 inches - so you can cut circles out of cardboard and go to Lowes/HomeDepot and drop the circles in -
a 7 ft will fit 4 but VERY tightly - making it difficult to insert/extract kegs. (been there, done that!)
the 8.8 cu ft model fits 4 on the floor loosely.
both will accomodate another keg on the compressor "hump" but you'll have to build a tall collar to account for the height of the kegs (about 25" plus connections)
I just finished my replacement (old one died) - shown below - so it can be done. Whether it's cheaper depends on your level of craftsmanship, your skills, and how cheaply you can find a commercial kegerator.
inside shot:
I have my CO2 inside the freezer, and the tank & lines along the back are for my glycol cooling for my fermentation tank. Now to build my pipeline back up - (yes, those are empty kegs)