I agree with everything Joel said above. The price of getting Trimix fills most places is usually reasonable. Here in St Louis, it runs $2.20/cf and that's if they have it. I consider that unreasonable. I have done trips where we brought/blended all our own gas, which worked out to be around 20sets of doubles, and I don't know how many stages. It is a lot of work. The gas, equipment, and beer can all really add up, but like Joel said, the main ingredient is time. You spend a lot of it setting up the system, getting the banks filled, mixing the gas, and getting the tanks topped off. A lot of times this winds up being outside in 15 degree weather. Some of it is enjoyable, and some of it isn't.
When you are doing it for yourself though, you have the peace of mind that it was done right, and you have the convenience of being able to do it anywhere anytime. You also learn a lot through the process. You also start to adapt your diving a little to make fills easier on yourself. IE, diving bottom stages more often so you don't have to remix doubles, and scheduling some nice 140' dives a couple weeks after the deeper 180' dives so you only have to top off your 18/45 to get some 25/25 going.
IOW, don't knock dive shops for charging what they have to to make money, and realize it does take work and effort to save the money by blending yourself.