@Merristasis There are two very different financially approaches to veganism, you either eat heavily processed food (like all the meat substitutes and whatnot) or not. The former is much more expensive, but the latter requires more time for meal preparation. If you go with the latter you should probably still drink some fortified plant milks, which are a bit expensive, but their cost should be offset by the lower cost of other food (pulses as a source of protein mainly). Other than that just remember to get some B12 supplements, and possibly D too (although you should've probably taken the latter regardless of your diet, if you are in non-southern France).

I also second @yojimbo 's opinion, you can do this in steps to easen the burder (although I quit cold turkey and it wasn't that hard either).