For Mining not for Data centers so anything that is reliable, can handle many hosts and fast is good. I don't think it need Enterprise level Routers but I could be wrong. The consumer grade routers, simply are not made to do that well above 80-100 hosts and that's already really pushing it since they are design for home at 15 or less devices.
For that many "host" (500x mining rig) you do need medium/big business routers, the switching and routing capabilities of home or even small enterprise routers is just not good enough. Also when you consider reliability having for example hot swappable/redundant PSU's, redundant WAN, it's great to have, if your router fall, the whole operation fall.
You didn't gave me much infos to go with. But if i take what my rigs use, and multiply it by 25x to reach 500 i think a 4321 or 4331 should be enough and you can find plenty of used/refurbished/brand new ones on ebay. But if you also route your home connection through it, you will be limited in bandwith because i presume you have a 500Mbps internet at least ?
Maybe a cheap alternative like the RV340 (~300$) could fit your need, but tbh i'll be more confident with one of the above even the smallest one.