You could get 150 with only $30 by buying 15 200-point DSiWare games (10-coin survey for every downloadable game). At most, it's three Wii games that you bought at full price more than a month after release, didn't Intend To Buy, and didn't do the Post Play surveys on yet.
Odd that Minis is 50 coins more despite both games selling for the same amount of real money.