Mark,
Welcome to the world of lightweight gear obsession!
Yes, it can get expensive, but it does not have to be if you carefully think about what you "really" need.
The more that I have ventured into lightweight backpacking, the more I am realizing how much I don't need to carry and therefore don't need to spend money on.
I think that what gets expensive is going to something lighter, then getting comfortable with that new bit of gear and then gaining the confidence to go lighter while remaining safe.
I have gone through 3 packs so far and might be moving to another one that is not necessarily lighter, but "better" for me. (In my case, from a GoLite Jam2 to a GG Gorilla).
My advice, spend a lot of money on your sleeping bag…get as warm and light as you can because it is one bit of gear that you can have with you for many, many years.
Myself, I have a Marmot Helium EQ 15F and a Marmot 40F Atom which covers a lot of range…sometimes I regret getting the 40 F Atom vs. the slightly warmer 30 F bag they make as I am a cold sleeper.
Anyway, my point is that much of the expense can be simply from re-buying new gear to replace stuff as you get lighter and lighter….given a little bit of forethought and thinking about what your mental level of comfort is, you might be able to avoid the expensive baby steps.
For example…for me, it was a complete leap of faith to go to a MLD ponchotarp & bivy setup, having never used either before. Knowing myself and my desire to go lighter, I jumped to it realizing that it was the only way to go to get superlight.
It worked out for me in that I skipped the whole transition from tarptent to tarp/bivy to ponchotarp.
Hope that this helps and good luck to you in your gear quest.
-Tony