For me I found some nice t-shirts on REI that has UV 50 protection near the bikes/tri/running section; ~$30. I'm fairly sensitive to the sun. They are quite tight fitting and much softer & lighter than the polyester t-shirts I used to wear for soccer; though a little more expensive.

I wasn't able to find any (cheap) bike t-shirts that has UV protection.

Was surfing around the net just now and found out they're supposed to be for wave surfing/swimming.