We currently have a project in which we need 1250 MAX models, which are in Max 5 format, updated to a later version
What do you mean by "in Max 5 format, updated to a later version". Do you mean you need models created in Max version 5, which you will the update? Or do you mean you have models that are in Max 5 and you want them updated for you?
Also more information along the lines of what Skyclad suggested would be very helpful.