I have used both No Rez and the DIY method on different speaker projects and like the DIY cost savings. Once I got got rolling the extra time was minimal because I had to use small pieces anyway with all the internal bracing to navigate and the 6" diameter speaker cutout everything had to go through.
I used 2 layers of self stick vinyl floor tile from Home Depot, 1" open cell foam, and 2 cans of 3M Hi-Strength 90 spray adhesive. My first test with the floor tile was hit and miss, some tiles stuck and some pieces fell off the next day, the 3M adhesive worked like a champ and gets stronger with age. I used the 3M adhesive to attach the 1" foam too.
5 - 24" x 27" sheets of No Rez costs $199.75 + shipping.
5 - 20" x 30" sheets open cell foam, self stick vinyl tile, 3M adhesive cost $84
The cost difference between the No Rez and the DIY method was $115.75.
Wayne