Turkey weights vary according to genetics, management, sex, and age. An example is shown at http://www.aviagenturkeys.us/uploads/2015/11/13/nicholas_comm_perf_obj_select_2015.pdf
You pretty much need a scale to determine the weight of the turkey prior to sale.
As for how much to charge, that depends on what you can get, which will vary between customer bases. City folk, for example, will pay more than country folk.
Make sure whatever you charge covers your expenses, including the time you put in raising the flock.
Also - are you selling live or processed. That will have a big effect on the price.