When using essential oils, be sure to stick with the ones that last in cold process soap.
This list needs some updating, but it's a good place to start. And, don't forget to check safe usage rates using EOCalc.com. I will try to find some time soon to update
this thread on eo blends.
The best way to save on fragrance costs is to do your research in advance and then test the FO using your recipe(s) and methods. SMF is a good place to start. Reviews on the supplier websites help, and I know that Nurture has a FB group. My biggest soap making disappointments over the years happened when I rushed ahead without following my own advice.
Brambleberry may be on the expensive side, but over my five years of soaping, their testing notes have been the best/most reliable of the bunch relative to the suppliers I've used (BB, WSP, Nurture, Oregon Trails, Majestic Mountain Sage, Fragrance Buddy, Scent Memory, BeScented). User reviews and photos are also very helpful. When I see a good handful of photos of nicely swirled soaps posted in the reviews, it builds my confidence that the FO is well-behaved across recipes.