I am currently making a trampoline, I am based in the UK so this may not be of great use to most of you but here goes.
I found a great company pointnorth.co.uk, I rang them and explained what I was after.
They reccomended using Trampoline Mesh, (Polypropylene basket weave, UV inhibited monofilament mesh) for the main body, this is then edged with PVC coated fabric (codes TM1 and P16). They also sell the grommets and will hire the tool to fit the grommets.
I approached a local boat cover maker who will stitch the PVC fabric to the trampoline very cheaply especially if you glue the pvc edging in place first which reduces the set up for them.
My trampoline is rather large approx 4m by 2m and cost me under £100 all in.
I haven't used it in anger yet but it all looks OK.