Just one song?
My rate is around $100 a day because I work with lots of different genres. Makes it easier for clients to see how much time actually goes into recording/mixing, rather than just a price tag on their shitty song. Extreme neo-tech-classical-death-prog would require something like a day for drum editing alone, and a singer-songwriter may need two plugins and some automation.
If someone from a "Template A"-metal band asked me how much it'd be to record a song, I'd explain to them that tuning and miking a full drum kit would be a complete waste of time since it'd take longer than the recording itself (same goes for amps etc) and base the quote off that. About a day for pre-prods, writing and editing drums. About a day for guitars, and then another day for bass and overdubs. Vocals should take a day if the vocalist's got his shit together. And finally, one full undisturbed day of mixing (editing is done while recording, otherwise clients can't see how much you're actually putting in). I'll normally spend two days since re-recording all their instruments sometimes takes longer than expected. Then there's mastering, which everyone just assumes comes for free. I refer them to a mastering service that charges about as much for mastering a song as I do for mixing it. Suddenly they're willing to pay that little extra.
I always include a couple of revisions on the mix etc (I'm a nice guy), but if they just won't trust me when I say that nobody's going to care that the vocalist breathed in 0.0002 milliseconds too early on bar 28 they have to pay extra for the time it takes to edit it to infinity and beyond. But if everything goes smoothly, the total would be around $500 if I'm not mistaking. For just one song. Without mastering. It may seem like a lot of money to them if it's their first time around, but if the guys are serious with their music they'll make it back with a single gigs pay.
It should be noted that I do this "off the books", don't pay taxes etc. Reason being I'm employed full time as a web designer, I just record bands in my spare time to help finance my G.A.S. lol
A funny story I feel is appropriate here: One time I was mixing a band (friends of mine). They'd done the recording themselves in their rehearsal space. Super shitty recording with lots of clipping over a EZDrummer track with about 5 hits at once on every bar. The editing took me forever since I was doing it in my spare time, and I really gave it a try since I want my reputation intact. When I was finally done, about a month later (!) I sent the final mix to them. I think we settled on revision 5 (super picky dudes), and two months had passed. We started arguing about the price, which I felt was a blow beneath the belt, since I was already charging them next to nothing because of the aforementioned friendship. "But come on! The mix took like an INSANELY long time to complete, we've waited FOREVER, we can't pay full price when we've waited this long". When I explained the obvious to them, other arguments against my super low price tag started to emerge. "Come on, man. We can't pay that much. We just put down like a $1000 deposit in a real studio, AND we've printed t-shirts and stuff". I'm no longer too sure about the aforementioned friendship.