That's what I have! I can boil about 6.25 gallons, but I watch it very carefully until after the hot break! I've only had one boilover, though, in the last 3 years or so.
Got a target local? Go to the kitchen section and look for an Imusa Tamale steamer. Its 8 gallons (32qt) and $18. That's what I use. I can boil 7.25 gallons in it with fermcap. Could probably go as high as 7.5 gallons but that's just asking for it.
Edit: Here's a link to it so you know what you're looking for.
I use a 30qt aluminum pot for 5 gallon batches. I've boiled a full 7 gallons in it without problems, but your do have to pay very close attention. I just grab a good cigar and a spray bottle with water in it and enjoy not having to do anything for a few minutes.
If you are patient, watch Craigslist. I snagged a huge 15 gallon brew pot with a pre-installed bulkhead fitting and valve for only $120 a few months ago. That sort of thing is $200+ new.
A 7.5 gallon pot is probably fine for a 5 gallon batch as long as you are careful about boil-overs. Just make sure not to boil more than 6 gallons at a time and keep the boil intensity low-to-moderate. If you would like a pot that's less likely to boil over, go with 10 gallons or bigger. Jumping to a 15 gallon pot like I did is nice, because it's not much more expensive than a 10 gallon pot, it works just fine for a 5 gallon batch (and is pretty much boil-over-proof), and it can also handle a 10 gallon batch easily.
I personally never ferment more than 5 gallon batches, but I recently had a little brewing party where I was able to do a full 10 gallon batch, and a friend who's very interested in getting into brewing got to take home a 5 gallon bucket of wort. His first batch of homebrew is going to be awesome, mainly because I did all the brewing and he just has to add yeast, wait, and bottle it.
I do 5.5 gallon batches with about 6.5 in the boil to compensate for boil-off in a 7 gallon aluminum pot with no problems. I was looking for the same thing, a cheap kettle to start AG. I haven't had any problems so far.
Smart and Final, if you have them, have aluminium pots for decent prices. I think their 32 qt is $70, and it's pretty thick AL. I have their 5 gal for my HLT and an 8 gal MegaPot for my BK.
Maybe it's just me but even my 8 gal kettle is too small for 5 gal batches and I wish I had just got a 10 gal kettle. It's fine for exactly 5 gal batches made with Pale Ale malt but if I use Pils malt (i.e. longer boils) and want to make a 5.5-6 gal batch I have to reserve some of the wort until it boils down enough. More than half of my brews use Pils malt and are more than 5 gal batches. It's really no big deal to do the wort/boil-shuffle but I just would much rather be able to put all the wort in the kettle and get it boiling and not have to piddle with it. I'm not a 'Purity Law' brewer but I don't want to have to buy another chemical to brew (so I'd rather not have to use fermcap).
If I could go back and do it again I would not even consider an 8 gal kettle no matter how cheap it was (well...almost). Get the 10 gal imo.
Yep the aluminum pots at Sammy's are hard to beat on price and they are fairly high quality. I have a restaurant grade aluminum pot which is 1/4" thick, which heats up quickly, is indestructible. A few dollars more but worth it in my opinion if you are going to use aluminum. Go through your local restaurant supply house to get one. Montanaandy
I got a 9 gallon stainless pot for around $75. Works great for 5.5 gallon batches. It's made by one of the turkey fryer/boil companies (Bayou?), just not the one that comes with a burner, which are almost always 7.5 gallons (which IS too small for comfort, from my experience).