Yes once you buy you will be able to sell or use in the Google Play store, you will need to upload yourself though.
A reasonable offer would be nice as quite a lot of work when into it, also you won't be able to re-sell the code if you do buy but you can do what you want with the app.
Would be better you pur a start price for such auction, otherwise people may ignore the work involved at such project and make offer as 0,02btc.Why dont you sell those at googla play by yourself?