You might find The Part Time Vegetarian useful as it has recipes you can make either way if you are phasing out meat:
www.amazon.co.uk/dp/B0146E4EW0?tag=mumsnetforu03-21
Pulses/whole grains are economical and you can use canned pulses if you find it easier. Sarah Brown's Chilli Bean Casserole is a perennially dish with meat eaters and can use whatever veg is in season:
craigloftus.net/chilli-bean-casserole
(if you ever find the Sarah Brown book second hand buy it - its excellent)
Meal planning will help with costs and variety in the diet.
General budget meals with veggie section:
[www.budgetbytes.com/category/extra-bytes/budget-friendly-meal-prep/vegetarian-meal-prep/
OhMyVeggies has largely gone to Insta but still has a meal planning section with shopping lists:
ohmyveggies.com/category/meal-plans/
VegWeb:
vegweb.com/
BBC Good Food and Allrecipes are also good options - bung in some ingredients and see what the search throws out.
In general I would avoid veggie books by non veggie celeb writers. Most realyl don't "get" vegetarian eating and are cashing in on its resurging popularity. I'd give River Cottage and Rukmini Iyer an honourable exception - they write useful books based around veg and fruit
Rose Elliot, Anna Jones, Bosh all write from a vegetarian perspective. Otherwise I'd look for good classic food writers who simply include a lot of vegetarian food, particularly those write regional books from the Med, Middle East, South Asia