I'm pretty sure the lowest, non-Prime, price at Rendo is $5 (same as the minimum checkout amount). Rather than using your own format, have you looked at using the DSON format for UVs? PoserPython can load a JSON file, as I recall, in one call (after which accessing items is just accessing members of an object and array) which may reduce one bottleneck, and it's a format that already has a bunch of files written in it.