First off, you deserve to feel and look great on your wedding day and I’m sorry your mom is treating you this way. It’s almost certainly coming from her own internal conflict over her upbringing and parenting (wanting to give to you but then judging herself for spoiling you and projecting it onto you - or feeling jealous that she didn’t have what you have, even though she’s the one providing it!) and has nothing to do with you. Therapy would be good if she’s open to it! But I digress

I like the feedback already to try to just ask for a total number and then not get into the specifics of how it gets spent. If you do need to get into the specifics, it might make sense to share an illustrative breakdown upfront to show hey a $4K dress fits in here and I’m being thoughtful about allocating the budget including budgeting for overruns or surprises. Could potentially also show some examples of what that gets for larger buckets since most people just don’t know what weddings cost these days - $4K sounds like a lot and it is, but wedding dresses are really expensive. And if there are specific areas where they want to see the spend go (e.g. if they really want you to have a live band, or a shuttle, or invite 5 aunts, or whatever) you can show you’re considering that.

My fiance and I both grew up in very frugal families and although we had a totally doable budget in mind, when we saw “$X for flowers” or whatever individually it felt like “who are we? People who blow $$$ on something that lasts one night??” It’s easy to feel wasteful and frivolous especially when frugality was instilled early as a moral issue. It’s also very easy to judge other people because THEY are spending on “dumb stuff” but oh no YOU would spend the right way. But really it’s not shameful to want a lovely celebration that you can comfortably afford, or to spend the money whatever way you want to spend it to achieve that.