What do you mean by cheap.. mass produced domestic?
If $5.50 is cheap, then I'd say Shiner Bock or Killian's. There is a local brew, Diamond Bear, (may not be avail.outside AR) thats really damn good for about the same.
Otherwise, I'd probably say michelob, then busch, then budweiser. Its been a long time since I've had any though.. maybe busch and bud would tie or their rankings would be reveresed.
If I had to drop below that level in quality, I think I'd rather buy PGA and cut it to vodka strength (or just cheapass vodka and filter it), rather than move on to stuff like mickey's, blue ox, schlitz, that one in the camoflague bottle.
I mean, if I'm drinking that stuff its sure as hell not because I enjoy it. If I just want to get fucked up that bad, I'd rather go ahead and accelerate the process and cut back on the suffering.