DIY:
-Buy new dremel blades for fiberglass
-Remove Cover, setup on saw horses
-Create a massive dust cloud, breath in harmful fiberglass particles
-Look at crappy engine cover, with felt mesh now embedded with fiberglass particles
-Sand down felt surface and create more dust
-5 hours later, paint or reflock engine cover
-install mesh on reverse, put back in car
-look at bad-looking cover, realize it looks bad, and throw it away
-remove engine cover entirely, or replace with aftermarket engine cover
Any kind of a DIY will result in a subpar result, a great deal of fiberglass dust, a wasted weekend, and 5-10 hours of your time. Perhaps you enjoy these kinds of projects, but as someone who started, and got 25% done with, this project, I would just buy something from cantrell, downforce, etc.
5 Hours of your time, possible health hazards from the fiberglass, and a giant mess, or $500?