Usually, if you are working with a Real Estate Broker, he or she would ask you to get you pre-approved for the price of home that you want to make an offer for.
And, you would need to let them know why you would like to have a Seller Carry back a contract.
At a minimum you need to see the inside of this home before writing an offer, and you really should look at comparable homes in the neighborhood.
Owner carries have many advantages, but they also have risk for both parties.
Before asking I wanted to make sure that you know in seller carried contracts that the $20,000 would be non-refundable. If for any reason you decided to not purchase the home that money would remain with the seller.
I will check with the owner to see if that is an option for them.