This an interesting question, and a complex one I think. First of all it depends on which country you are based in, and how common it is to find high quality 3d images.
Obviously the reasons for this are the average wage level for a particular job, and supply and demand for the service you are offering. In the UK prices vary massively, and depend on a number of critical things. First of all the size of the completed image, whether you want a photomontage (exteriors only), how much additional modelling needs to be done, how good the quality will be, and what the timescale is.
If you are really fantastically good, like some people on this forum
you can charge what you want. In this respect it is a bit like any element of art or design - many people make a choice based on quality first. For the most part though, if there is a lot of competition, and the market is fairly small, you will have to either make your work cheaper, faster or better than your competitors, or give them something that no-one else does. For example, easy to deal with, asking fewest questions, and the ability to almost 'read the client's mind'.
If you choose someone to design anything for you, you want to explain to them what you want, and for them to go away and do the work really well, and fairly quickly, come back and see almost exactly what you wanted. Then maybe you will make some corrections or modifications, and you will have a fantastic piece of work. Of course this is a very simplistic analysis because some people (perfectionists) like lots of contact and control, but others don't want to be involved at all.
I know this might not be helpful, but as a guide, I can give you some UK examples.
1. For a whole 3d site of 200 acres, modelling the buildings and terrain and producing a DVD with a 3d fly-through cost approximately EUR30,000. The model was untextured. Quality was not brilliant, and I think this was overpriced.
2. For 3d exterior photomontages of a city centre site in London, at an image size of maybe 5000x5000, for an almost perfect visualisation, for a single image including paying a professional photographer to take high quality photographs of the site and modelling from 2d AutoCAD drawings, took 5 weeks and cost roughly EUR 6000. Quality was outstanding, but expensive.
http://www.futurerealities.co.uk/index.html
3. For a series of interior views (stills), from no 3d data at all including modeling, rendering, texturing, post-processing, each image cost EUR 600.
Each example is from a different company, but don't forget that there are large international bureaus specialising in this thing now.
http://www.idrawfast.com/ is an example, and they are quite good. Their quality is nowhere near the best, but they understand the business very well indeed.
I hope this has been of some help - good luck!
