
OK how about this - if you have easypopulate installed on your site, and microsoft excel or some other spreadsheet software on your pc you could:
(DO A FULL BACKUP OF YOUR DATABASE FIRST)
1) download the easypopulate model/price/qty file
2) open it in microsoft excel
3) copy the column "v_products_price" and insert after the original one
4) in the first row, (assuming "v_products_price" is column E) type "=E2*1.10" (without the quotes. whereby 1.10 again is a price increase of 10%, amend if necessary)
5) copy that code, select all the fields in your new column and paste
6) save the file (as .txt, don't change to excel), close it and open it again (that converts the formula you just inserted into actual figures which zencart will understand)
7) delete the original "v_products_price" column, keeping only the one with the new increased prices

upload file in easypopulate (if need be get easypopulate to split the file up, 3000 products will probably cause it to time out before it's done updating all of them)