I don't really know.
Both are now considered "used" or closeout boards, so I'd check with a few shops and see what kind of deal you can make.
Be sure you are getting a 2008 Rio. The '08 Rio is much different than the earlier Start based Rio's from '06 and '07.
Since you are only 62 kg. you might want to look for a Rio S as it's slightly narrower and has 175 liter volume which should be more than adequate if you've been sailing the F-138.
Where are you located (what country)?
Hope this helps,