I see great value here. This is a really short name, and a topic that can serve many people.
The name is vague enough that the site could be developed in a number of ways. I think your first priority should be developing in any way to get traffic to it, because the .com variation is undeveloped.
petdogs.com has been registered for 9 years, and is for sale for 75k. This is an absurd price, so we can't use it as a reference - but your domain has actually been registered slightly longer, and it's to your benefit that petdogs.com is undeveloped: the market for the name is up for grabs.
The downside that i see for this site is that generally companies prefer their brand be part of the domain name. Interested buyers may end up being people intending on turning it into a profitable directory of sorts.
I would set an asking price for $5000 (or $3000 if you're in a rush), and take the first offer over $1000 (or $500 depending on your expections/turn around time).
You may also consider approaching other existing sites that may be interested, such as dog adoption sits or dog supply sites. If you want to put this time and work into it, you could actually get one of those larger figures above.
Good luck! I hope others appraise for you too, we have quite a bit of variation between the first two appraisals!
