I haven't tried their cabs, but I've bought some other things from Seismic, cables and the like. If the cab quality is anything like their cable quality, run like hell. There's a reason for the price. The other recommendations so far would be the way I'd go. I've never heard a bad word about Avatar and sometimes they have great deals on their closeout page. Great customer service too. Heard good things about Stagecraft too.
If you're patient, there are always deals to be had on craigslist, especially post holidays when people need to pay shit off. I bought a loaded Marshall 1960s for $175 and got an old 1982a cab from the 70s for $300. There are some other sleeper cabs I see pop up cheap too. Don't be scared of certain Crate Blue Voodoo cabs. They are baltic birch and some (not all, do your research) are Celestion V30 loaded. I've seen those go cheap.