I went a couple of years ago and stayed at the Mirage, it is a truly amazing place - but expensive (even more so now with the exchange rate!) so budget accordingly.

A sunset helicopter flight into, a picnic in and flight out the Grand Canyon was a couple of hundred!

There is some stuff you can do for free - all the casinos try to outdo each other so you can watch the dancing fountains at the Bellagio, a 'volcano' erupting outside the Mirage etc. etc. and easily kill an evening or two that way.

Only other thing i noticed was that there's nowhere to eat except inside any of the hotels/casinos. Not even a McDonalds/Cafe/Coffee Shop to be seen!