This is basically a pre-pro single not like it's actually getting used on the EP. We're going to a big studio at the end of summer to record the full thing. Why would I want to blow $200 for mixing on one song that isn't gonna be on the final version?
$200 is still rather low for editing, mixing and mastering a track. About 1/3rd of what I would expect the rate to be from engineers I work with.
For the person doing the mix it's exactly the same process, time and amount of effort no matter if it's a single, album track or if you're never gonna release it. It makes no difference to the person doing the job.
This is why I laugh at people who ask me to "just do a quick mix of 30 seconds of the song" as an audition for the job. Explaining that mixing a song isn't a linear process and that song length has very little to do with the amount of work is very difficult to do.