This is nit-picky, but I think reframing your question will help you get the result you need.
Having a mentor and figuring out how you will pay them feels like a contradiction since I've never had a mentor that ever asked to be paid for any advice they gave me.
Finding a mentor is a very organic thing in my experience, and definitely worthwhile, but I think the shortest path to getting to a 7 figure revenue rate is to get a consultant that can help you improve your skills and better focus your resources.
You could do this by leveraging them in a group setting, like masterminds, you could retain them monthly, or just about any other format they're open to.
I've got a client right now that is in a very similar spot as you, doing $350k and just needed some guidance to get better focused on what will get them to $1MM. Our arrangement is with a weekly call and he's asked for more help, so we're moving my deliverable work under a profit-sharing agreement.
I'd use Clarity to talk to a lot of different consultant's and see what you find. Just don't jump into an long-term agreements until you know they're a fit and are more interested in your success than their fee.
Practice with me for free if you'd like and I can help you get your questions dialed in better for future calls: https://clarity.fm/joshualong/VIP