I wouldn't recommend flipping santas/h'weens. F2p have access to those as well and so you have more competition.
There are very few f2p people who can afford rares.
All rare items are obtainable and tradeable by f2p's.
If you have the money, go for merching rares.. Good luck!
How well does Pernix items work?
Flipping santas from August to Christmas makes excellent profits.

