Congratulations on your winnings I still think, you should consider betting with Bitcoin and I will give you an example why.
Lets look at the over/under at wbet7 for tonights NBA game Raptors vs Bulls. Line is 207 with equal odds for over and under of 1.81. This is just a very bad payout of about 91%. But since you want to bet with Ethereum, you are stuck with this bookmaker and his shitty odds.
If you now use Bitcoin instead, you can get the same bet with odds of 1.95 (or more), which is a huge difference. Imagine you place a bet of 100,- Euro (or whatever your currency is), you will win 14,- Euro more, than you win with wbet7. From these 14,- Euro you can easily pay the transaction costs you mentioned earlier.
You are literally giving away a lot of money just by only wanting to use ETH.
It is good point. I understand all about fair odds, I am new in crypto betting but I have a long career on traditional sites (finished last 10 years with modest profit from betting with 10% tax included) . Wbet7 has rather shitty odds. My favorite site for fiat serious bets is pinnacle sports. Which site has those odds you mentioned? I am especially interested if it is also offering tennis handicaps in their book. Tennis and soccer are my main sports. Never gotten into basketball unfortunately, I know quite a few people making good money on it(at least claiming).