Something very easy and one of the best way to get charms would be to ice burst rock lobsters. Some stats to give you an idea: I bursted rock lobs for 84-99 mage and it got me the charms for 88-99 summoning. To spend less cash on the runes, I highly suggest using battle robes with sol, it saves half of the runes. I also had a tome of frost, so didn't need any water rune. (also used arcane steam but that's up to you!) Also, instead of having inventory full of ppots at the start of my 3k casts trips (battle robes fully degrade in ~6 hours trip, which is approximatively equivalent to 3k bursts), i brought a full outfit that gives prayer bonus (to pray melee during the lures). Switching from battle robes to proselyte is a must, but i also brought my SGS, and specced a dagganoth every now and then for prayer boost. That way, i only needed 1 or 2 prayer pots for 6 hours trips ;) If you have anymore questions, feel free to add me in-game :)