Supply and demand really is what drives this price. Your looking great on the supply side of things, considering their are no freebies out there that are 3 numbers. But the demand isnt the greatest either. If you are lucky and find a buyer who just has to have 717.com, then, you are in very good luck.
Otherwise, alot of 3 number domains are for sale for prices around 1000 - 2500. I like the symmetry of 717, which I think helps its memoribility. Repeating numbers are also good, for example, 955.com is asking $1000. Another domain 030.com is asking $2500.
So anyways, I'm thinking 1 to 3K is a good end user price.
How are your offers comparing to these numbers?