I figured it out before that 1 gram is about equal to the cm on 3d hubs. So I set my price on there as such.
But it all depends on the infill used.
I have a file I did for someone that is 102 cm and it used 93 grams with solid and another was 4.5 cm and used 7 grams with full but if changed the infill I would got about 5 g. So I have it listed as $10 start up to cover discrepancies and electricity plus I ask them to pick the infill but they never do. lol
When I first signed up on there and other sites I couldn't believe what they were charging but you don't want to go too cheap as it will possibly alienate you because people will think its cheap for a reason so you want to underscore but still stay within the average pricing.
On my website I offer services way cheaper than on the 3D sites. lol
Don't forget about your time.. If you have a large part with light infill it can still take hours to print.. I think I have mine at .75 per cube cm. A 24 hour print gets me about $150. About average for this area. This company I deal with eats it up as the injection mold they will making costs about $25,000.