I second P. punctatus. 10+ dorsal rays indicate Pterygoplichthys.
Interesting to see one so large, though. Rarely are individuals of that size offered, as the cost of export/import typically exceeds the projected market-value in proportion to demand of the fish at the country of destination; and seldom does anybody take the time to grow one out to that size in an appropriately-sized tank over the course of several years. Small juveniles are not too uncommon, but adults tend to be rare.
I think they are quite attractive, and certainly not worth casual dismissal. Fun fishes in their own right; bold, hardy, etc. Though I may be somewhat biased as I used to buy tiny punctatus fry to grow out.
The weberi-group is also typically labelled 'properly' (or rather, with more attempt to label down to sp.) for commercial export as they have some ornamental demand/value, instead of being lumped in with other misc. Hypostominae. In that regard they tend to be one of the less-mislabelled Pterygoplichthys, so it is interesting it was sold under the moniker of 'cactus pleco'- inclined to think that was a mishap on the store's end.
The price is not terribly problematic. The fish looks wild-caught.