With 124 art pieces, even if you were to discount every single art piece to 3 USD as the discounted commission cost, that still comes to 372 USD minimum. Add some give or take in case some pieces are gifts or free event prizes or even cheaper than the discounted example number of 3 USD per and you're still looking at 300 USD minimum if you really wanted to sell him for cheap.
With 124 art pieces and all the time and money it took to amass that quantity, 300 USD is the least you could ask for on a sale. That's still a massive steal for anyone interested in the design since any character coming with that much art off the bat is basically a dream.