Lets see , return flight 16-20k depending on season and how early you book
accomodation cheapest is dorms which is good for solo travelers 7k max
if you move to an island i would suggest to use flights and carry baggage big enough to fit inside your cabin baggage allowance i.e 7kg, to get cheap air tickets and save time.
so another 3k to and fro the island
daily expenditure 1.5-2k which will come to 14 k max
so all in all total of 50k you can have a good trip although i would suggest to utilize the 15 days visa you are paying for and extend your stay. you can save up by staying in hostels and getting beds for as low as 500