A lot, it's better off to get fire runes from the grand exchange for 9 coins each or craft them at the fire altar near the Duel Arena in Al Kharid (fire/omni talisman/tiara/staff required to enter). If you have extra fire runes, sell them at lowest price and it should work in a couple of hours. Fire runes are in low demand and it should buy immediately if you ever want some.
or if you want, it's pretty easy to get fire runes from flesh crawlers in the 2nd floor of the barbarian stronghold
Also fire giants drop fire runes in like 150 increments so thats a good way too