1) stamp duty payable on purchase of property is as per ready reckoner rates
2) even if you purchased property for 23 lakhs you will have to pay stamp duty on Rs 50 lakhs as per circle rate
3) value fixed is not final but only a prima facie rate prevailing in an area. It is open to the registering authority as well as the person seeking registration to prove the actual market value of property. The authorities cannot regard the guideline valuation as the last word on the subject of market value.
4) you can submit document to collector for adjudication of stamp duty . The charge ability of stamp duty on the instrument as determined by the Collector of Stamps is not final. The person affected by the order of the Collector of Stamps can go in appeal to the Chief Controlling Revenue Authority, Maharashtra State, Pune as provided in section 53 of the Bombay Stamp Act, 1958, limit prescribed for the filing of an appeal is within 60 days.