how long is a piece of string?
costing depends on numerous things. ie...
* you as an individual - how good are you and the service you offer? is this a one off job for extra pocket money, or a going concern for your business? are you a nube with no experience or name, or have you come recommended and you're a big cheese in the business (meaning you can potentially charge so much more)? do you generally charge per job or per hour? what is your location and overheads? what's the general going rate in your part of town? (i know location is less relevant these days in the age of the web, but even so, it matters)
each of these factors greatly effect the price.
* the brief - you haven't really given us much to go on. if this job were offered to me i'd ask for a fair bit more info before i give a quote. if this was all i had i'd give a quote based on previous similar work i've done. and i can almost guarantee my prices will massively differ to yours.
what's the dead line?
is it just a modeling job (as you seem to indicate) or do you need to provide stills/animations too?
what quality is the client expecting, photo real or more schematic/wip?
how complicated is the job? (modeling furniture and kitting out an interior might be time consuming).
will you need to charge for extras? (ie, render farm costs, photography costs, printer costs, cd/dvd costs etc etc)
see what i mean? i know what i'd charge (given more info) but i'm presuming you're quite new to this and just in it for a bit of extra cash. my charges wouldn't mean to you. so sorry, cant give you a figure
why not just determine how long you think it'll take you and charge the client a figure that'll make you relatively happy for your time taken?