How to build my prototype to production (Kickstarter, etc)

but the in-software purchase options seem quite expensive.

To be honest I didn't try that. You can export as gerber though, which you can use with DirtyPCBs and OSHPark, both of which are extremely reasonable.

Fritzing isn't that good really, but I think it's a lot less of a learning curve than something like Eagle (especially as it has many of the modules built into it already).