90-99 wouldn't take too much cash or time I can't give you an estimate right now unfortunately, because prices are MUCH different than when I chinned to 99.
I would also go to Ape Atol skeletons and skip mummies, just to get more bang for your buck. Ape Atol will give you far more exp, although you won't get any drops at all. Mummies take much longer, and can be a total waste of money if you don't spend the time luring them into a 3x3 square for maximum exp. The only advantages of training at mummies is that you get some small drops though, such as ancient staves, rune scimitar & square shield, small gold items that you can sell or alch, and a few charms I believe.