I suppose you could "back into" low-carbing, but in my experience, going "cold turkey" breaks the cravings much more effectively. After the first few tough days of withdrawal, I was much better as far as thinking I "needed" bread, etc.

As for expense, I find I actually spend LESS on groceries. I shop on sale for meat,(and cook ahead for quick meals during the week)and have gotten creative with eggs (and I really used to HATE eggs). Since I don't buy as many convenience foods, frozen dinners, etc. as I did before, I've made up for the fact that pasta and potatoes are cheap "fillers".
The bigest challenge is cooking those starchy foods for family members not eating lc. I generally make JUST enough for them, and encourage THEM to help with food prep by making those dishes for me. (especially if my "resistance" is low that day...)