This is the question that everyone wants an answer to but at the same time it is one of those things where its hard to depict a universal response.
There are many ways to come up with how much you want to / need to charge in order to grow your business and not "slave away" at 5$ per hour. But you see, that right there is just one of the problems you will encounter. For me, working at 5$ per hour would be financial suicide and I'd probably get an equal amount selling ice cream down on the street with the difference being I can do that for 8 hours a day while freelancing is not that stable - at least not all the time - which means selling ice cream would be financially more beneficial for me. Then again, 5$ might be ok for someone operating from Asia where their living costs are lower which means they can afford lower salaries. The same goes for US <-> Europe.
I think for starters you need to figure out how much you need to survive based on the number of projects you are getting or are hoping you will be getting (be realistic). A link like this
http://jironomo.com/architectural-visualisation-blog/2010/04/how-much-does-a-3d-rendering-cost/ and this
https://motivapp.com/freelance-hourly-rate-calculator MIGHT be helpful.
Of course, the other thing is learning about the prices people usually put up which is something you are trying to get an answer for right now. Well, it is hard to say and it differs from project to project but me personally, I've done projects where a value for an image was as little as 200EUR and as much as 3000$. It is of course different if you are working in a studio vs being freelance but you get the idea. There is an interesting thread going over at CG Architect about prices, might be worth a look ;)
The best thing would be for us to post images and specify what the price what but even that might be a little off - sometimes clients give you 3D files, sometimes you get DWGs and sometimes you get concepts - at least for me that makes a difference when giving out a quote on a project.
Unfortunately I don't have much freelance experience doing stadiums so I have nothing but theory to share.