Haasonline is pretty reputable around these parts, and the site claims that the bot supports Bitmex, though licenses for the trading bot are only for 12 months, and pricing currently starts around 0.073
BTC for the beginner setup. More pricing details are available
here. The basic license is sufficient for most IMO, and you don't pay any extra for the bot to trade on more exchanges, as even the basic bot supports all exchanges the bot is capable of.