This calculates the profit/loss of paying Thormac to change a battlestaff into a mystic staff. It normally costs 40,000 per conversion, but this is reduced to 27,000 when wearing a Seer's headband 3.

Battlestaff Battlestaff
staff cost
(no headband)
Air Air battlestaff8,211 Mystic air staff24,384 -23,827 -10,827
Water Water battlestaff8,298 Mystic water staff24,117 -24,181 -11,181
Earth Earth battlestaff8,442 Mystic earth staff24,236 -24,206 -11,206
Fire Fire battlestaff8,227 Mystic fire staff24,297 -23,930 -10,930
Lava Lava battlestaff9,220 Mystic lava staff44,352 -4,868 8,132
Mud Mud battlestaff31,629 Mystic mud staff68,077 -3,552 9,448
Steam Steam battlestaff29,281 Mystic steam staff82,367 13,086 26,086
*Note: You can buy up to 100 battlestaffs of a given type every 4 hours in the Grand Exchange.

Warning: do NOT expect any of these to be profitable. They normally sell for well below the GE asking price.