The complete kits are dear as they can contain stuff you may not need or already have like a back-cap, ceramics, tungstens and collets but all the parts are available individually and it can work out cheaper to just get the parts you actually want.
A stubby gas lens will be the best mod you can make for that torch. Farrrrrrrrrrrrrrr more useful than clear Pyrex cups and waaaaaaaaaay less costly too.
I have 1 Pyrex cup and it's been put on about twice for a job where I've had to stub the torch right up to weld a bar inside a tube and I couldn't actually see because of the ceramic. This was where it was actually useful as a welded it by looking through the cup (not easy but doable).
You'll find 9/10 people put them on with out actually been able to give a reason why they do. (Makes my torch look good) well that's all very well till one day you forget to turn the gas on or your torch slips off the bench then all of a sudden that looking good novelty soon wears off when it's cost you £15- £20 for a new one that your likely to smash again. To me they are a purpose serving tool that will come out of the box to be used when the situation demands so I'll always keep one. I wouldn't buy them to put on for my usual work mind. The way my torches get knocked about any profit would be chucked into ck or furwick if I did that.
Just my opinion.
you can use reservoirs from e-cigarettes as they are dirt cheap in comparison, but you'll have to work out what size you need. here's one I fitted to a wp9 torch,held in place by a silcone O ring
although I never really used it in anger, but the pyrex tube was less than £1.20