Haunted Mine, What Lies Below, Tree Gnome Village, Vampire Slayer, Lost City.
Every game lasts 6 hours and will get you roughly 90kxp for Attack, Strength, Defence and Hitpoints.
70-99 is roughly 136 full 6 hour games meaning you will spend either 272k if you host it yourself, or 3m if you pay for hosts.
The cost of repairing the Guthans 70-99 will cost you about 18m.
Hope this helps and I didn't fuck any calculation up.