IMO it's a bit hefty but if the fish is good looking, go for it. They are not difficult to breed so if you spot a pair, I'd suggest to grab them quick.
I love Red Head Tapajos, but in Singapore, we have good supply of this fish, and the price is USD13 to 15 for a fish of that size. However, a show specimen would fetch a much higher price as there are collectors who would pay top prices for a good fish.