[steve-k]

its a question of quantaty, unless like decowarrior you have a source you will need to rent 2 cilinders  at about 5 per month each, medical grade has an introduced moisture content, that in theory can accelerate the decay of your tank, and also is only charged to 130barr breathing grade is charged to 230 barr and is only slightley more expencive,
we hire o2 if we are going on trips where there is a high expected use or the local shops dont offer a fill
apart from the relevent course you will need a filling whip (£250-£300) And an o2 analiser (£200) +60 a year for a new cell

you can also have the problem of shops doing a top-up of clean air, especially when you try to explane why the finished cooled pressure is so important, they become verry reluctante,

i never atended a blending cource befour i mixed my own, i suppose you need to determin your own level befourhand, and decide what course you need

conclusion
unless you intend to ues nitrox on every dive, it is not worth the finantial outlay and running costs to mix your own nitrox, it becomes more feasable if you have a diving partner to share with, furthermore it can be a bit of a hastle, and is so much easer to just drop your tanks off, then to pick them up filled,
all this said we run a trip down south where we rely on our own o2 because of thr time constraints of the local shop, we 1/2 our deco penelties by filling our stage cyilinders with our own o2, we even get it delivered to the local pub  lol