Just following on what Relic said..keep in mind you're talking about basically two different types of remixing here..
a)..the PRO kind, where you get somebody "established" with their own business and studio, to remix your work, in which case you're going to be looking at a fee.."standard rates apply" as they say and that can mean either by the hour or by the track..as well as any "extras" you want included, such as preparing formats for certain services, mastering stems, burning to disc / disk and the likes. It can really add up fast.
b)..the "AMATEUR" kind, where you get somebody who's "not established" and usually working "out of the box" to remix your work. Most times this can be for free, in return for a public credit and/or a small sum of cash, if you feel they've done a good job you're happy with.
That said, don't be surprised is some amateurs charge you a fee, too..and there's nothing wrong with that, as long as you get what you're paying for and they know what they're doing in the first place. I nsuch cases, you're talking about folks who've usually "served their time" producing their own work and the work of others for free, all the while perfecting their production skills.
Fee or no fee, the end result from getting an amateur to do it for you can be just as good in every way as if you went with the services of a PRO..the only difference being they are trying to become established and might not have all the gear / hardware a PRO might have..but that doesn't necessarily mean their work will be crap because of it. That said, it's still a good idea to be familiar with that person's work..both their own and any work they've already produced / remixed for others.
Regardless of which "type" you go with in the end, make sure you strike up a good level of communication with whoever it is, as you don't want to waste either your time or theirs, due to everyone "not being on the same page" from the start.
Give it some thought and explain clearly to them what it is you want and expect them to do and make sure you understand everything they say to..don't hold back on asking questions if anything is unclear in your mind.
Personally, I'd suggest that when the time comes, you start by posting an ad in the IDMf classified section on here, asking for interested members to PM you..or even reach out to those on here who you think might do a good job, based on what you're already heard of their own work and see if they'd be willing to give it a go. There's some really talented folk hanging out on here and you could do a lot worse than engaging one of them for the job.
Best of luck with it.