See this:

http://www.indiegogo.com/projects/keep-skullgirls-growing

The total cost to add a professional-quality 2D character to a fighting game is $150,000.

The animations alone are $30-$40k as shown by their cost breakdown.

I don't think you can commission this for less than $10k and get quality results.

What Clint said about $10k minimum matches my calculations almost exactly. :)

Assuming you want to do something cel-shaded like Skullgirls, you're probably looking at $50 per frame on the low end.  Counting up the frames that Cammy's sprite uses in Street Fighter, I came up with just about 200.  (Note: ripping these sprites or using ripped sprites is illegal unless you have permission from the game creator; the above link is included to illustrate what I'm talking about.)

That being said, if you want to go with a pixel art style, you might be able to do it for somewhat cheaper.  The Street Fighter characters are (from a quick glance) less than 100 pixels high.  I've paid as little as $150 for pixel art sprite sheets, however, there are a couple of caveats:

• I've never commissioned anything over 64 pixels high.  Past that, things start getting expoentially harder and (by extention) more expensive.
• None of the sprite sheets I've commissioned have had more than about 50 frames of animation, and generally somewhat less.
• Street fighter sprites are way more complicated.  In a lot of the sheets I've commissioned, many of the frames are similar enough that they can be created by copying a frame and then editing it, rather than redrawing the frame from scratch.  However, if you look at the link above, you'll notice that Cammy's motions are very dynamic, which requires a lot of each frame to be redrawn from scratch.  It's possible (and even quite likely) that she was cel animated first (at the same cost that Clint mentioned) and then converted to pixel art by hand.

So, in short, if you don't mind taking a hit on quality, you might be able to get an experienced pixel artist to put together a smaller sheet with less moves and vastly simpler animations for $300 (miniimum) or so, but regardless of the artist's skill, there just isn't a way using pixel art to approach the quality and fluidity of the Street Fighter sprites without spending a lot more money.

That being said, I don't think there's anything wrong with being realistic for your budget.  Your game doesn't have to have street fighter quality animations to be fun to play, and the sprites themsleves can still look nice.  You might be able to find an artist who can help you at that cost.

Disclaimer: IANAPA (I am not a pixel artist), so my prices are guesstimates based on what I've commissioned in the past.  $300 may be low, but you could certainly do it for under $1000 per sheet, if you're willing to cut the corners I mentioned.)

So, finally, a brief word on 3D characters.  A high poly 3D character model can cost around $2000 or more.  I'm not particularly familiar with how much it costs to animate them. but I'm guessing that if you're looking for something like in modern fighting games, it can get really expensive.  Regardless of whether you use motion capture (in which case, you'd have to hire acrobats and martial artists who can pull off the necessary moves convincingly) or 3D animators, but either way, to get the animations looking right, it would require a lot of testing and tweaking, which can really add up.  Most likely the animation process costs more than the models do.

Again, though, you can cut costs on this.  Low poly models can be had for significantly less money; you might be able to get one rigged for $300-500.  After that, you could do the animations yourself if you don't mind the tedium and the fact that it's just not going to be as good as if a professional does them.

So, in conclusion, I don't think it's necessarily *impossible* to make a Street-fighter-like game on a shoestring budget, but to actually match SF's animation quality and number of moves, you need a lot more than that.  What's interesting is that the difference in cost between a really ugly looking game with programmer art and a decent looking game may only be a thousand dollars or so, but the difference between a decent looking game and a really professional one that feels smooth and fluid can be in the hundreds of thousands of dollars.

One last thing: There's a slim possibility that you may get really lucky and attract a large fan base.  If you do that, you might be able to harness the time and talent of your fans to improve your game over time; however, even with very good games, this is a rare occurrence.