depends on the letters.
example....
qwz.org may sell for 30$ while crm.org sells for 500$
Normally crappy letters such as q,w,z,x,y,v usually go for 25$ to 60$
Depends on the combination. 2 letter .org are nice also. You can find nasty combos for around $30 nice combos like xxx.org might run you in the thousands.