If you are staying near Shilin, there's a camera store eWhat nearby (
) Looking at their website, the 75mm costs about 29900 NTD now. I would also suggest you go check out Bigcamera (
) which is just beside Shilin station. Bo Ai area is not a bad choice but things can get tricky there, you will need some patience (you either get great deals or cheated.) The two stores I mention have greater transparency in prices. Hope this helps.