I would not pay too much to customize an oscommerce site. Many of the most commonly installed functions on oscomm are ALREADY installed on the free Zen Cart or CRE versions....this is the point of these platforms whcih is to give you a more robust version of oscomm that you dont have to customize as much.

So...if the features he is adding are already on other free carts...why not start with those.

Do you NEED monthly customizations? If you are going to pay $4000....i would want the programmer to install interfaces and controls so YOU can easily make changes and such without needing the monthly fee.

It is high...but he might be REALLLLLLLLY good. If he is custom designing all kinds of graphics and flash and things for your site it would add to the price...but i dont think you really need to go that high unless you really like his graphic design styles and think he is worth the extra expense....You can also pay $100 to $200 for an '"off the rack" template if you dont really have a big custom design need.