What is the opposite of "free" as in "free of charge"?

A person, animal or thing that is not free could be any of the following:

bound/bonded, grounded, restricted, captive, enslaved, shackled, reserved, occupied, busy

Examples:

• Are you free? No, I'm busy.
• Is this seat free? No, it is reserved.
• My people are still enslaved. We want to be free.
• Some are free, but some are still captive.
• I don't know when I'll be free to visit. I'm grounded indefinitely.
• Our Southern brothers are free to do what they want, while we Northerners are bound by archaic and stifling conventions.

I just reread your question and realized I wasted my time writing all these answers, since you are only interested in the commercial case. Anything that is not free is simply not free or for sale. If you want no more than a single word, however, a few options are:

billable and chargeable

Paid

Paid would be my choice. There are free services and paid services. (The latter are services that are "paid for".)

You need to check if it suits your context, though. You have not mentioned the sentence where you would like to use it.

Probably the closest is a two-word compound, for sale.

• That's not free -- that's for sale.

It would presuppose a commercial context, though, like free.