its not just the .pz3 but every texture, geometry, etc.  some scenes and their related files could get up to a gig.  even if you could compress that before transfer to use 1/10th of that its still a lot of back and forth data....  and the licensing issue would still present a problem.

btw if renders bogging down your comp is a problem - have you considered putting together a dedicated rendering box?  the price is not that prohibitive, and in the long run it would save money over paying someone else/renting server time to render. i dont even have mine hooked up to a monitor, it just sits in the corner and i access it via remote desktop.

assuming you use onboard video (perfectly sufficient for a rendering machine), toss it in an old case and hook up any old HDD you have laying around (its not a good time to buy HDDs right now):

Phenom II X6 1090T boxed processor - $165
8GB DDR3 1600 - $30
Antec Neo Eco 520W PSU (rebranded SeaSonic) - $50
midrange ASUS ATX mobo - ~$80
Enzotech MOS-C10 mosfet heatsinks - $15

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~$340 + tax.

the boxed heatpipe cooler on that Phenom X6 should get you to at least 3.8ghz on stock voltage, and equates to impressive rendering performance.  you could put something together even cheaper but i wouldnt bother.

if a remote rendering service charged only ~$25 a month,  you could build your own little rendering box for roughly the same cost for one year.