l was backing out and on the turn l bumped my front bumper and scraped the rear side of a white lexus rx330 (05 model)... some scrapes and some color came off, no dents... its about 12x5... l was willing to pay off for the damages and l was wondering how much would it usually cost to fix it at the dealer?

If they want to paint the whole bumper it will probably cost about $300-400.

depending on the quality and paint color, $150-400

you need to get estimates from body shops. you are going to end up paying for wherever the owner wants to take the vehicle, as they legally can.

Your best choice is a body shop.
You will get a better price because Lexus charges a higher hourly labor price. Plus, alot of dealerships do not have their own body shops.