what to get? how much?
A couple of questions. I am planning two road trips in my head. The first is from the Sacramento area, where I live, to Michigan and back. The second is up to Alaska. I have been considering getting a rental car of some sort. Who offers the best deals? How much would it cost me to rent a car for a trip of 4-5000 miles? Will rental car agencies allow you to drive a car one-way, such as from Sacramento to Anchorage or Fairbanks, and fly back? Need info.
You'll find that different companies will have the lowest rates at different times -- search for the best rates using travel-reservation functions like Travelocity, Orbitz, etc, and there is one on this site you can use. You can also find great deals on the companies' own web sites frequently.
It is key to reserve ahead of time as the best rates are usually not available at the last minute. Some companies will rent one-way, but the costs are much higher as they will charge a "drop" fee. For a trip as you mention, your best bet is to rent by the week, or even month, depending on how long you intend. You can often find small cars for around $100 per week plus taxes and fees, full-size cars are available at times for $150-$200, if you get lucky.
Finally, I am reluctant to recommend anything other than than big national companies -- a cheap rate isn't worth much if a company adds extra (and often unexpected) fees. The worst experience I ever had was with Thrifty -- they charged over $300 for a bb-sized parking lot ding. I'll never rent from them again (especially since I knew for absolute certain the ding didn't happen while I had the car). As you might expect, Hertz is often more expensive but I have never had a serious problem with them -- they typically offer first class service and there has never been a hidden or unexpected charge. I feel that's worth paying a bit extra for.
Unlimited mileage but read the small print
Many rental companies offer unlimited mileage but often the small print restricts the range. Many also are using GPS tracking to see where you've been. I rented a car in Vegas last year with unlimited mileage that charged a penalty if I crossed a state border. Califoria was only 30 miles or so away. No I -15 South for me.