I thought the smaller sizes of Jo Malone were comparable in price to "Beautiful", etc?
There are soooo many perfumes for you to choose from! But the thing is, your search going to have to take place in the "middle", with fairly "safe" scents.
Estee Lauder do a "Private Collection", which includes "Tuberose Gardenia" - this is available in a handbag size; so rather cheaper and less committable-to. It's bright, floral, with great sillage and lasting-power. I think it would be an easy step for your MIL from "Beautiful" to this, and "TG" is less 80s.
Dior do a set of "Escalier" perfumes which are floral, citrussy, and lovely.
A really beautiful perfume, modern but with a family likeness to the ones your MIL likes, might be "Iris Nobile" by Aqua di Parma. (I may have spelled the perfume house incorrectly there.)
I love the way your MIL has a "going out perfume" - I used to have that, back in the days when I "went out". I think Hermes "Ambre de Merveilles" is a lovely "going-out" perfume.
Sigh. I had hoped to be given perfume for Christmas this year.
All of these are available in John Lewis or another good-sized department store.