Is there any harm in buying fish from different pet stores and putting them in the same tank at the same time?

no. the same concepts apply, dont overstock (including stocking too fast), make sure the species/sizes are compatible, avoid diseased individuals. but in general the fact that they are from different stores shouldnt have any affect on your success witht them.

If these fish are going into an empty aquarium, there's no problem. If it's an existing aquarium, then you might want to quarantine the fish beforehand to reduce the chance that the new fish might bring something in. The only downside of combining fish from different stores that are just bought is that there's a greater chance of one carrying something which it would then give to the fish from the other store as well if kept together.

Oh thats good since their all going to be in an empty tank.

I was reading up more about bristlenose plecos and i found a really cool one! the Starlight Bristlenose Pleco (L183 or L182 they called it for some reason). I wanted to try and get that one but I couldnt find a price range anywhere. Does anyone know how much they sell for?