It's labor-related.
That extra $55-100 per hour adds up after a 8 hour install on most 'power adders.'
If you don't mind a little dirt, then wrench on it and save yourself an awful lot of money.
I tinkered with the VQ in my Maxima and pulled plenty of extra power out, and only had $2 or 2.5K invested. Admittedly, I wasn't running juice or boost, but even that SHOULDN'T be 5+ thousand.
You're tuning a widely available and tinkered with basic import car... not a supercar that requires a mastertech.