I completed my SuperGrafx collection late last year. My copy of Aldynes cost me 13,500 yen (with a beat up cardboard sleeve), and my copy of 1941 cost me 19,900 yen (without the sleeve). I honestly feel that I got a pretty good deal on both of them given market prices.
But yeah, $300+ for Aldynes seems pretty excessive. I can see a copy for 14,000 yen from an online store in Japan, and you can probably save a good 20-30% by finding a copy on YJA.