bptraveler, there are inexpensive packages from IcelandAir Vacations including departures from MSP. We paid $499 including RT air, RT FlyBus, and two nights at the beautiful Nordica Hotel with an incredible breakfast buffet. We bought several Excursions which were well worth the money, particularly the evening departure to the Blue Lagoon. Your Mom will have a ball!

gohaggis, it is expensive but not as much as you think. The FlyBus was 1100K which works out to US$15. You don't need a car because you can walk anywhere or take the local Straeto busses for 220K, or buy a Visitors Card which gets you into all the local museums, pools, spas, and buses for just US$15 a day. Yes, the food was expensive, but incredibly delicious.
Considering the IcelandAir package, the whole trip was a deal.