propane torch.. the poor man's autoclave ;)
$25 for hives with 2 10-frame deep brood chambers, all frames, etc., included? I'd be all over that provided the wood wasn't decomposing. Quite the bargain (I'm assuming he'd also have covers, etc., etc.,).
I'd clean down to the bare wood (frames included) as much as possible then thoroughly disinfect (w/alcohol, hydrogen peroxide, ionic nano-colloidal silver soln - no toxic residue, but you could use bleach too & thoroughly rinse) - maybe finish with a good spray coat of essential oils (lemongrass, etc.,). No pathogens should survive but there still might be (limited) traces of pesticides in the porous wood. I would think it would be minimal and pose little if any risk... but I still might be inclined to have a "guinea pig" colony test one hive before using more.