I don't see too many really low fares to LV anymore. If you do get them, they are quite restrictive re what day you can fly, etc.
Anyway, we live in SW Michigan and I know that Allegiant Air flies direct from GRR to LAS. It's a discount airline that doesn't always show up on the Travelocity-type of sites. I think Sun Country flies out of Lansing as well, so that might be another one to check.
Our "low" airfares for LAS for the past few years have been because of using frequent flyer miles and/or credit card promotions of buy-one-get-one. We have driven to Detroit and flown Spirit airlines, but lately I find they aren't that much cheaper than flying out of GRR.
If you just have a single flying from GRR, I'd try to stick with flying from there or even Lansing. If they don't mind the drive, Flint is another airport that's not too bad.
So, you just have to subscribe to some travel sites and be a bit flexible. If you can't, you'll probably (at least for the GRR flight) end up paying $250-$300 for the RT flight.
For the hotels, I would suggest scouting those out ... I try to book something that can be cancelled, so will book directly from the hotel's website. As the time gets closer, if you are there during a slower period, the rates start to go down and/or they start to put offers out there. But the weekends (Friday & Saturday nights) will be more than weekdays. Don't forget that all of the MGM/Mirage properties will have a resort fee of as much as $20 a day. The Ceasars/Harrahs properties do not have a resort fee.
I don't think you need to get a car for the short time you are there; however, would suggest that you stay on the strip if you don't have a car.
Above all, I would suggest you get the "Unofficial Guide to Las Vegas" and/or the "American Casino Guide" ... lots of good information regarding getting around LV, what to see, costs, etiquette, and how to play the various games.
Read through some of these LV posts, as I've put a few links for websites for coupons and such.
Good luck!