You may be shocked at Lowes and Home Depots prices too. Be sure to factor in installation when comparing prices. I've heard that's a major hidden cost. They also now have quite a few different grades of modulars too. Start with cheap particle board boxes and a natural finish and upgrade from there, if you so choose.
I've been around the business (mostly on the finish end) for close to 30 years and have always been surprised at what it cost. Just the wood prices alone may knock your socks off. And then labor to design, build, finish and install it..... Geeesh! Keeping it simple and more straight forward can save some bucks. If you get too crazy and extravagant ya just gotta dig deeper. lol!
Luckily I've been in the position to trade out work for anything I've wanted...... That reminds me.... I need to get a picture of my tool room progress.....
It'd be interesting to know how large the difference is between cookie cutter cabs and custom. Keep us updated.
There's always IKEA's cardboard cabs too..........