Cleaning an xbox dvd driveThomson dvd laser replacementPhillips laser replacementSamsung laser replacement
Cleaning your laser costs nothing, but doesn't always fix the problem.
Replacing you laser is cost effective if the rest of the drive is working fine (motors, tray, etc....) Under $20 for a replacement laser.
Replacing the drive is the most expensive, but also the easiest to do (just plug & play). Even thomson drives have gone up in price lately and you'd be lucky to find a good working one for under $30 on ebay. If you want a brand new one... expect to pay over $40.
If you want a better drive than the Thomson.... expect to pay even more (up to $70 for one).
You have many options to fix disc read errors. Start at the least expensive one and work your way up.