Michelle,
FWIW, there is a Platinum Oceanside Barony unit on Redweek.com with asking price of $23,500 (most people feel you can negotiate). Most units on Redweek.com are FSBO. One drawback to Redweek is that most listings don't provide complete information, i.e. view (oceanfront, oceanside, garden at properties that price that way), week or season, etc. You would have contact the lister to find out more details.
You should check out the Right of First Refusal (ROFR) database for Barony. It shows that a Platinum oceanside unit passed ROFR at $19,200 (posted 5/16/08). The price Marriott exercises their ROFR is a moving target, but at least this gives you an idea. Here's the website link:
http://dioxide45.tripod.com/cgi-bin/rofr.cgi
Buying re-sale definitely takes more work on your part, but in some cases the savings can be substantial.
If this was your first time at a timeshare presentation, I would definitely rescind, take a step back and do your research, especially here on TUG. There is a lot more to using your TS successfully than the sales people lead you to believe. If after your research you still want to buy from Marriott, they'll always be there ready to make the sale.
BTW, how many points did they say you would get if you turn it in for points rather than use in a particular year? My brother bought a platinum unit (garden) at pre-construction and he gets 125,000 points. Just curious if they have lowered the point value since then.