The prices are whatever you're willing to offer.
Whether you're offering 1, 100, 250, 500, or 1000+, it's completely up to you.
More specific requests get better results, or at least closer to what you're expecting.
Higher offers attract more talented artists, but you have to sort through the crap and ripped art at any price range.
For example:
Offering 400 fg
Topic: whatever you want
Preferred colors: black and red
Renders/Stock images, or samples of what I like: provide links
Text: whatever you want, if any, possibly a preferred font too
Type: 400x150 traditional, borderless, animated, w/e
What I don't like: monochrome, low quality, animation, text, w/e
Best attempt wins / buying multiple sigs
If you don't know what you want, shop around for premades
Premades are sigs that were either made with no specific person to sell it to, or made for someone else but didn't sell
You should probably also use the right forum:
https://forums.d2jsp.org/forum.php?f=111But it looks like the community here died away and isn't complaining about requests in this section as much as they used to