At our airport hotel, we can call some nearby private companies we know about and have a car delivered to you at the hotel AND you can just leave it in our lot when you are done with it for generally $40-$50 per day. The advantage is that you don't have to go get it or return it yourself, dealing with airports, shuttles and trams.
Or you can call an Enterprise or equivalent company and they will come pick you up and deliver you back to the hotel. The downside is they have restricted hours and can't bring you back after certain times or you have to return it to them and wait for a ride to the hotel. Also, their rates are usually not much better than what the hotel can get it for. Our local Enterprise office is not open past noon on Saturday or Sunday at all, so forget turning the car in on a weekend and/or getting a ride back to the hotel, much less renting one on Saturday afternoon.
You can take a shuttle back to the airport, take a Tram or van to the Car Rental Center or lots and arrange for your own car at the myriad of choices at the airport. Generally, the rates per day are better because of the competition under one roof AND you can rent one online at an even better rate and just go pick it up. The downside is airport 'fees' and 'surcharges' are added on so a $19.95 per day 'deal' may really come out to $30 or more for a one day rental. Plus, YOU have to return it and then reverse the trip on the tram/van back to the airport and then call for the hotel shuttle. This takes about one hour as a rule, so if time is money, add that to the supposed savings you get.
Off airport properties are the lowest of all as a rule, but also the hardest to deal with. You might have to GET there on your own or at the least take the shuttle/tram to the car rental center and then wander outside to a staging area and call one of the off airport outfits and wait for THEIR shuttle van. I did this myself last summer and while it is the most time consuming, I got a car for only $15.95 per night.
Lastly, you can call "Rent a Wreck" type places and get a car for under $10 per day BUT you will likely have to get there on your own and back again, so add in cab fares and keep in mind they are NOT open late as a rule, so forget dropping off a car at 10pm and getting a ride home. Some of these places are so out of the way that even getting a CAB to come get you is difficult.
In the end, you have to decide how much convenience means to you and how much the daily cost means to you. The real break comes in renting a car for multiple days - that way you spread cab fares and extra airport surcharges over the whole cost of the rental. If you opt for a Car Rental Center choice, remember so do dozens of others. So waiting in line is almost mandatory as it is for returning the car and many times the economy car you desire is sold out and only more expensive SUV's or intermediate cars are available. So you might end up spending more than you had planned on. Plus you will have to schlep your bags and possibly your family on shuttle vans or trams back to the airport. In the end, being able to return the car to the hotel instead of a rental office might be worth the extra $10 you spend.