Look do what you want. You bought an "expensive" exhaust, you cant tune it because you cant afford it. You have 2 options:
1) Put it on, dont tune it, run rich, maybe glaze bores and do damage, maybe not or;
2) Dont put it on, save, get a tune with it.
No point continuing on. They are your options, you can piss, moan or otherwise but the fact of the matter is, they are the options you have to make a decision on. Noone can make a decision for you.
P.S. GC8 Pryde, for 40k you could of bought an unmodded gc8, thrown a 207 in with an
ECU,Fuelmods, a deadbolt/IHI turbo, tuned, with coilovers/swaybars/antilift kit/fully sprayed for less. Id of gone that path, but like someone else said, each to their own.