Glasses or Contacts?

Three friends need glasses. One wears glasses, one wears contacts, and the other wears special sunglasses that can also become regular glasses. Figure out who wears what and how much they paid for their corrective eyewear.

Clues:
1. The sunglasses are 3 times the cost of the glasses, but the contacts are half the cost of the glasses.
2. Dennis spent under $200.
3. Alice spent more than Serena, who spent less than Dennis.