Not music related but I have had a few significant electronics projects made in recent years (I was designing and building electric cars for an endurance series). I found there are three types of electronics engineers, 1, good and reliable, 2, good and unreliable, 3 useless on all fronts. 2 and 3 outnumber 1 by at least 10 to 1 if not 100 to 1. Even with a very defined end point and most of the board designed (it needed specific style of voltage transformer adding) it was a nightmare getting anyone to quote. It was a fair bit more complex than a pedal to be fair but two prototypes on hand etched boards were just short of £1000 to get to useable point. Final boards came in at £280 for design and set up costs and £5 a board thereafter for small batch run. I think the £280 was only that low as the company was very interested in the project and saw it as a toe in for a different sales area.
if you can do some of the development costs you will save yourself a packet. If we had needed someone to design the whole PMT board as well then cost could have been £5000-10000, but you are looking a level of complexity similar to an amp I guess.