I've run into the same wall with my own projects. The differential in cost between a one-off ARM board of medium complexity compared to even a higher-complexity dev tool made in decent quantity (gumstix, rpi, beagleboard) is just amazing.
What I've noticed is that there is a step in cost once you hit a certain level of complexity. Markup on parts is pretty predictable across the board, but the fabrication costs jump once you exceed the capabilities of the hobbyist-friendly services. OSH Park will do 5 mil trace, 4 mil space, 10 mil annular ring, which is about the best there is when it comes to inexpensive one-offs. That's enough to break out some of a 0.8mm BGA. To improve your capabilities with components that size or smaller, you need to look elsewhere, and suddenly you're looking at "real" services and now the prices are in the several (or tens-of) thousands of dollars range. That's the point where a hobbyist can no longer approach this stuff. Now you're investing in prototyping and you've got to have a business plan.
At least you can get a System-on-Module. That seems to be the only way forward unless you have lots of money to sink up front.
What I've noticed is that there is a step in cost once you hit a certain level of complexity. Markup on parts is pretty predictable across the board, but the fabrication costs jump once you exceed the capabilities of the hobbyist-friendly services. OSH Park will do 5 mil trace, 4 mil space, 10 mil annular ring, which is about the best there is when it comes to inexpensive one-offs. That's enough to break out some of a 0.8mm BGA. To improve your capabilities with components that size or smaller, you need to look elsewhere, and suddenly you're looking at "real" services and now the prices are in the several (or tens-of) thousands of dollars range. That's the point where a hobbyist can no longer approach this stuff. Now you're investing in prototyping and you've got to have a business plan.
At least you can get a System-on-Module. That seems to be the only way forward unless you have lots of money to sink up front.