Hello there,
I'm Ringeman from Blacksmith Services and we might be able to help you with this.
80-90 str : 33.602.640 gp
80-90 ranged : 33.602.640 gp
80-90 magic : 84.006.600 gp (done thru high alching) (if you want a other method, these are our prices for that Splashing - 8gp/xp, Teleporting - 20gp/xp , String Jewellery - 10gp/xp, Bake pie - 20gp/xp, humidify - 15gp/xp, Tan leather - 30gp/xp, Superglass - 25gp/xp)
for the slayer part : these are our prices for that aswell : 1-50 - 250gp/xp (must have cannon) 1-50 450gp/xp (no cannon) 50-99 - 100gp/xp (burst/cannon) 50-99 230gp/xp (no burst/cannon)
ETA will be around a couple of weeks
you can always add me on discord ( bompa113#9809 uid 190874065781784576) or click my signature if you want to talk more!
and have a great day!