Coming from the kegerator side to the homebrewing side (got tired of not being able to find any decent brews in this beer desert I call home) I can offer the following advice. While this may not be true of all those that have used/are using the cheaper units, this is from my experience and a lot of reading.
The "cheaper" kegerators (anything around $500 and under) all pretty much come with the same common problems. Spend a little more (I think the Sanyo units, a few others I can't recall) and you get better results. Spend a lot more and you get pretty sweet results (think, True, Beverage Air, etc). Common problems with the el cheapos....
1) Temp control - some get plenty cold, TOO cold, and a bump of the control causes a ten degree temp swing; some don't get cold enough, even with added fans, and require more work. Most that I know with these cheaper units, at some point or another, end up going with an external control (Brewers Edge, JC, Ranco, etc).
2) Tower size - very small (in diameter) towers that are not "forced air" cooled. Assuming they have room for a homemade cooling system (pc fan, copper tubing) you can add one pretty easy, and fairly cheap. If you ever decide to change out the shank or want to add another tap, though, you're almost forced to look at a larger (3") tower.
3) Cheap components - not so much in the way of the regulator, but the faucets, shanks, and keg couplers (the latter you won't need anyway if using cornies). Most quickly find that as you upgrade one component (like say, the faucet) you end up replacing the shank too, which requires boogering up that tower that I mentioned was too small.
Again, much of this is from experience and forum reading on the kegerator side. I'm not trying to sway anyone from buying anything, or call anything that someone might be happy with "junk", but giving some advice on what you might expect to be ready for if you go the cheaper route. I started with an Avanti for just under $400 on sale at Best Buy. About $300 and a lot of time reading and tinkering later, I ended up with a pretty sweet rig. Of course now that I'm moving to home brew much of that (two top of the line Sanke D couplers and a bag full of gas and liquid tail pieces, for starters) is worthless. And with this unit I think I will be limited to two cornies flowing at a time. Not having to hear my beer store guy say "no, I can't get that either" will be worth every penny wasted though
If I had it to do over again, knowing what I know now (homebrewing or commercial kegs) I'd take a decent sized chest freezer, add a temp controller and a tower (or maybe do the collar trick) get the rest piece by piece, and be happy.
Happy Brewing (and happy drinking)!!