Shout out to Munich! Die besten bier der welt!
Prices vary wildly. But I've paid $80 for a 3-inch model (with lots of undercuts).
To be honest, you should figure out how much you value your time at, how many hours you think you'll get out of your solidoodle, how much filament you'll use, and how much it costs for you for power, the computer, the extra room in your apartment, etc...don't forget a profit for your business, you'll need to buy a new computer and a new solidoodle someday.
e.g. (1 hour at $20) + (1 hour / 500 hour lifespan of solidoodle = $1) + (100 grams filament = $3.50) + (overhead = $10) + (profit=$10) = $44.50
I'm pulling those numbers out of my wazoo, (I have no idea yet about the lifespan of the S2, or how quickly it prints). Anyway, those are the types of thing you need to consider.
If you want to go from the other direction, many of your "competitors" have automated quote systems. Download their quote software, or upload your model...then underbid. The obvious danger is that you may end up not covering your time, expenses, etc.