Altered Art Cards: What value should I expect?

Unfortunately, most US vendors do not purchase Altered Art cards. The ones that do tend to grade them as "Damaged" (Even if they're otherwise in pristine condition) and so at best we'll see is 25% of Near Mint value given. So while, yes, we can accept them, in most cases you'll get better value soliciting offers from some of the various Facebook groups that deal with Altered Art cards such as the High End MTG Alters group. There are numerous others, so your best bet would be to solicit multiple or find one the fits the niche your Altered Art cards belong.