Quick answer: Ask your Realtor.
Slightly longer answer: Make an offer.
Still longer answer: It's not unreasonable. If there are comps for sale at 314 and 319 (they're not really comps since they haven't sold), that means those houses are worth LESS than 314 and 319. Otherwise, they would have sold. The real question is: Are there comparable properties that have SOLD in the past 3 (or, at most, 6) months? Those are the ones to look at.
But if those houses at 314 and 319 are truly similar to yours (same neighborhood, similar age, similar style, similar size, similar lot size, similar condition), then the homes you're looking at are worth less. How much less? Impossible to say.
Recognize, however, that the sellers may not be able to accept, say, 310 for the property. That's their problem. Your problem is making sure you don't overpay.
Again: Check with your Realtor.
Hope that helps.