You may also try talking to the bank which owns the property and get them to finance it at the agreed to price, or else the deal is dead (assuming you have the appraisal clause mentioned in previous answers).
Evergreen Real Estate
This could present a dilemma since the bank had to do an appraisal or BPO's to execute their foreclosure. If you or your lender had an appraisal done that came in under the contract price, you should present this to the seller immediately.
As previously stated, your lender will likely not underwrite your loan if it does not appraise for at least the purchase amount.
If you planned on paying cash then you would want to have written in an appraisal contingency.
Of course, this question may be addressed in the addendums you would have signed at the time of accepted contract.
Check with your agent! They are there to represent you and help you in this process.
No professional can render an opinion on behalf of another party
Lynn911 Dallas Realtor & Consultant, Loan Officer, Credit Repair Advisor
The Michael Group - Dallas Business Journal Top Ranked Realtors