Best "affordable" bag for '81?

[ca180]

So, I want to bag my truck (long bed) for a moderate slam... I plan on doing AOL in the rear and using SD bag brackets up front.

But what bag can I get for a low price? Firestone on ebay or some other site? What size? 3000 lb? 500 psi capable? I have no clue. I'm new to the whole bag industry.

Anyhow, someone clue me in. I have searched as much as I can, but I keep coming up with endless pointless threads that don't pertain to anything I need to know.

Thanks guys