so i have been riding my DB response sport for a little over two years now and i have no complaints considering the price level of the bike (i paid $250 used) but i have been thinking about upgrading. unfortunately a new bike is not in the budget and most likely won't be for a while. my plan is to gradually upgrade parts through online sales, swap meets and eBay. What i am looking for is suggestions for the most value per dollar parts and what you think should be replaced first. i will be doing all the work my self so shop fees won't come into the picture. i am also not trying to go to crazy with the $$$ i would like to stay under $600.

This is the stock bike.

http://www.bikepedia.com/QuickBike/B...port&Type=bike