but there is not that much to congratulate him if he bought the tickets as he has spent over 12 Bitcoins to get just over 10.
This is wrong.
Even if the winner has purchased all the tickets (which doesn't seem to be the case), he/she has spent only 1.2175 BTC for buying them, not over 10 BTC. Each golden ticket costs 25,000 satoshi.
4870*0.00025 BTC = 1.2175 BTC
If the winner has earned all the tickets through wagering, he/she wagered 24.35 BTC for earning those tickets. You get 1 golden ticket for every 0.005 BTC you wager.
4870*0.005 BTC = 24.35 BTC