I'm surprised that the shop charges different prices for different percentages. The place I went to had a flat fee for tints of any percentage. Regarding the prices, I think the quotes you got are fair, if the shop is indeed reputable. You get what you pay for with tints. $420 is way too much, and $100 is ridiculously cheap. With that said, I would get the 20%, but not tint the windshield.
