I can think of only two such scenarios. One, if as part of your acceptance, you included an item that was not appurtenant(not legally permanently affixed to the property), e.g. a Baby Grand Piano in the living room that was not included as part of the price in the listing. Even if you agreed to the listing price, in such a case, your signing of the offer would be a counter-offer under law. Their read here increase in price would also be a counter offer.
The other http://www.utahrealestate.com/ scenario would be if the increase in price was "delivered" to you before your price offer was "received." Delivered and received are legally defined by applicable real estate contract law.
If neither of these occured, you could sue for Specific Performance and should be able to enforce the original Offer to Purchase and Contract that you http://www.realtor.com/ signed. If in doubt, contact a local Real Estate Attorney.