250 sprites or 250 frames? Some artists charge per hour, some charge per piece. Anyways, per frame on an animated sprite is like 2-5 bucks each if they charge by piece and not by hour. By hour who knows, depends on how much they get done which is based on artist skill/complexity of the sprite. It could take one artist 3 hours to deliver a fully animated protagonist sprite-sheet (complex) while it takes another artist 3 days, quite a big price difference.
Musicians often charge per 30 seconds/per minute, prices go up greatly if actual instruments are included. I'd say for a 30 second loop you're looking at maybe 40 dollars average, for a 1 minute trailer theme maybe 60-100 dollars. Sound effects are around 5 bucks a pop. Some musicians have different growth per minute, so the first is 30 dollars, second is 50, third is another 60, so for a 3 minute song it would be 140 dollars, as opposed to a musician doing a flat rate of 30 dollars per minute where the end price would be 90. These prices are based on electronic music. Electronic doesn't mean beeps and boops, you can get fantasy-themed violins and pianos that are electronic and sound great.
So, it's very iffy. My advice, shop around a bit in the portfolios.
So, realistically, a lot. I wouldn't expect to find a reliable, competent artist who works for less than ~$30/hr. If we imagine you hire an artist at 30 and they can turn each sprite in two hours (!), that's ~$15k.
You might get super lucky and find the triple threat of someone who's cheap because they're young/dont know how to price themselves, undiscovered, and actually experienced enough to be reliable/dependable... But I wouldn't bet on it. Maybe you can squeak in close to $20/hr in the pixel art scene cause their rates are weirdly suppressed. I know some phenomenal pixel artists who work that cheap, but it's pretty weird -- the skills they have could be reasonably quickly converted into traditional 2d art or Ui skills where they'd make vastly more, so you should consider finding one unlikely.
People throw around numbers a lot lower than that in the indie scene sometimes but... That's basically entry level wage in the grownup industry. Excuses are made involving cost of living in certain parts of the world, etc. But if an artist quotes you something halfway under the going rate they'd make working for johnny mobile games, you need to ask yourself: Why would a professional artist price themselves lower than what they could make from another client?
This is sourced from:
-Bunches of my friends and acquaintances have been on both sides of the professional freelance artist arrangement.
-I do art for a living (although I should note -- any numbers I'm giving are general, and not my own)
-forum posts and general experience
-The gamasutra game industry salary survey:
http://www.gamasutra.com/salarysurvey2014.pdf which, note, is for in-house jobs, where the artist gets benifits, ISN'T paying more for health insurance and ~30% out of pocket taxes, and has stable work.
250 sprites, that is the upper limit of the required number of sprites I'd say, as I'm going to be doing some work on sprites myself. Quite a few of these sprites are likely to be derivatives of each other also e.g. yellow colored turret, red colored turret, etc... That will bring the time required down considerably I'd imagine. I'd also expect quite a lot of the sprites to be single framed e.g. for walls.
Also keep in mind the nature of my game:
As you can see I'm keeping most things square shaped but I'm hoping to compensate the blocky visuals with a very detailed and distinctive art style.
Hypothetically would this be a good offer:
£1000/$1600 =
Protagonist sprites
Environmental sprites e.g. walls, floors, plants, etc... (4 Tilesets for 4 zones)
Enemy sprites e.g. turrets, lasers, spikes, etc...
Splashscreen
Menu/UI
Would be a reasonable offer to cover the art asset requirements of the game over the 3 month time frame considering the artist only needs to work part time to complete everything on his side?
Thanks for the information on music prices also. Those seem reasonable to me and I don't think I'll have a problem with them.