It is already there at

[bsrsharma]

It is already there at patrick.net

see for example, http://patrick.net/index/search.php?zip=&target=&downpay=&br=&ba=&start=350

For non-real estate transactions, the one I know is priceline.com

see http://www.priceline.com/promo/toughlove.asp?irefid=HPFEATURE&irefclickid=ToughLove_NYOPHotels_070907

P.S. I haven’t used either and I am not recommending!