Yeahhhh, that is the correct ammount. You pay however much the entry fee is to enter the room and recive 80% of your opponents entry fee plus your entry fee if you win the match.
So, for this example: (10,000 x .8) + 10000 = 18,000.
If you or another player are recieving more coins than that, it is from an apparel bonus that awards coins (MAX and Topgolf)