Are there any database changes in 2.0.5? I would have guessed not, that the only changes were in the interaction with the db (meaning the php source) rather than actual table changes. If that's the case, your bigger worry is the changes to the db that you may have made with the mods.
Here's the primary question... did you document the changes made for each mod?
I keep a record of any database changes in a different directory, named by mod, just so I can keep track of the changes that are required.
You said that you didn't want to "buy" another database from your provider, I'm assuming, then, that you have a limit? Because the easiest way to do this would be to set up a second board using 2.0.5, import your users and whatnot, and then start modding from there. You can also have some test users help you test out the new install while continuing the old board. Once you have everything verified, then you can switch the board from your old board to the new one with (in theory, anyway) no down time. It may be worth the extra cost for a month, just to save yourself some aggravation.
Or try setting up your "new" board at one of the free hosts just to get it going. Or set up a server at your house.
It doesn't take much to run apache + php + mysql, I have a server at my house now running linux and all of the above on a 400 MHz PII with 128 MB of RAM. It's just fine for a test / dev box.
If it were me, I would not wait for 2.2, since there is no firm deadline other than "when it's done". 8) Food for thought.