You'll find different types of prices depending the artist, quality, type of work, style, etc. here on the Forum, there are several artists always looking for jobs.
As well, you'll have to clarify your concept of cheap regarding if it's for personal use, non-commercial or commercial use, if it's printable, etc.
For example, my price is $110 USD for 2 characters and background. Extra characters would cost $30 each one. Image size around 4000 x 4000px. I don't demand royalties, you can print and sell your finished product and there is no need to credit me.
However, you'll find people with higher or lower prices regarding their work. I recommend explaining more or less what is the kind of work the person has to do, if it's more enviroment or character. Your budget mostly and then, people will offer to show you their portfolio and prices if it's according to your indications.