yeah, for money, runecrafting air runes is the best way to do it in freeloaders world.
OMG OMG OMG OMG!!!!
I LEARNED THE SPECIALIST LITTLE SECRET THE OTHER DAY... >.>... <.< ... ^.^ ... v.v ...
ok, as everyone has said, casting curses is the most cost effective exp in the free world, but it is also the same for members =P buy bodies and waters from rune stores. however many bodies you get, get twice as many waters. then get an earth staff. load yourself in full iron armour, or full mage armour, it makes no difference overall, and make your way to varrock castle. you know that random monk of zamorak caged in behind the stairs that you always wondered about when you were a newb? well, i learned his purpose.
this creature is a very unique being. it is the only npc in all of runescape with a defense level of 0. yep, zip, nothing, nadda, kein, nilch, zero. conveniently for you all, that means that its defense cannot be lowered. so if you cast curse on it, and it hits, it takes a milisecond to process the non-decrease in defense and the non-return up to 0 defense, allowing you to immidiately cast curse on it again, even if you just successfully weakened it. =P

and so on.
the practical upshot if this is that you can sit there and cast curses on him non stop, failed or successful, and thus you will never have to wait for your target to become uncursed or dead, like you would at scorpions or varrock sewer. with about 3 seconds per cast, if you had 10000 casts (i have that many bodies in my bank right now =P), it would take you about 30000 seconds, which is roughly 8 and 1/2 hours to get the 205k exp from those spells, including 10 minutes of error from the occasional successful curse, which stops the next curse from coming, hence losing potentially 3 seconds.