How much do CG renderings cost?

Hi, I have a good friend who is a struggling Architect and he would really like to have some CG renderings and a short 1 minute, 3D fly-through model of a building he is bidding on to design for a client. He admitted that he does not have the skill set to do the renderings or 3D work for his project, but he believes that would really impress the client and thus get him the job. -- I really want to help him, so I offered to do them for him as long as he doesn't want more than I can produce with my intermediate knowledge of 3D art work. I also told him that I would do them at no cost. -- I am not an expert in this field, so I don't feel comfortable charging for something I do not do professionally. I simply want to help my friend and get some exposure out of it.

That said, I'm curious...how much does a CG rendering cost and how much does a 3D model with a fly-through camera cost of a small building?

How is that calculated? - Is it by the size of the building? - Is it by the number of floors? - Is it by the square footage? -- There has to be a formula that the pros use to be able to quote a CG rendering or a 3D model with a moving camera.

Does anyone have any insight into this topic? Can someone guide me to a web site where pricing your CG work is discussed - maybe with some examples?

That said, I assure you I'm not going to charge my friend for the work I'm doing for him...I simply want to know how much something like that is worth - out of curiosity.  I also don't want to ask my friend how much its worth, because I don't want to make him feel bad that he can't pay me. I don't want to make him feel like I'm fishing for money.

I've done some research on my own, but have not found anywhere where a pricing formula or pricing structure is discussed.

Thank you for your guidance!

Fulano