I use the ASUSTOR AS4004T, It has 10GbE and it only cost me $359. It has 4 bays, it should be enough to check your needs and funds.
If you use SFP and RJ45 mixed, QNAP has a switch that has both for about $500. Otherwise, Edimax has an all-rj45 switch for $593 on Amazon. Aquantia also sells 10GbE cards for $79 on amazon as well. They're the best price so far.