I think that all depends on the fish, I am very opposed too paying $240 for a L142 or $180 for a L081/L018 when they are around 30-40mm, they are nice fish but that seems ridiculs especialy when HFF advertised a L081/L018 for $100 last week. So including shipping it would be cheaper to get a pleco sent down this way instead of driving into town and buying one. I love the fact that finaly we are getting some fancy plecos in town, but I think because they know there is only 4 shops and 3 others dont/wont stock them they have marcket monopoly and will charge what they like.
As for plecs to breed If I buy a group for around the $200ish mark and I do get them to breed to start with I would be looking at swaping the off spring with others that have plecos that I dont currently own, then depending on the fish around the $30-40mark is fair. If breeding for a bussiness then charging more to cover cost's is fine, but if your only breeding for a hobbie, then just making some extra coin to buy more fish works for me.