IMO you can do way better on the PSA 10 rocket dark magneton. I wish I still had the couple that I graded as 10’s. I sold both for $50-$80 in the past year or so. Even the charizard doesn’t normally go for quite that much.
I would look to pay no more than $60-$80 or so myself if I was looking to buy it. Actually I would probably just buy a sealed rocket box again and grade all the holos. Depending on how bad you want it though I guess $100 or a little more wouldn’t be terrible. Though, if you would be happy having one for $250 then there is no issue with that. Just figured I’d let you know from what I saw it seemed high.