What is common here, in the handy crowd at least, is to do your own electrical, plumbing, gas work and leave it open and accessable for a licenced professional to check and sign off on.

You're still paying for an hour or two of their time and a surcharge for "taking on the responsibility" but it's often not an issue if the work is clean, to current code, and sanity tests correct (correct wiring, correct angles on plumbing, pressure testing on gas pipes).