Please do not take offense but in my option you are on a fools errand!
In purchasing plants you often get cheap when you buy cheap! Good quality things cost good money. How do you know that the cheap isnt cheap because it is hastily dug up material without a proper root ball? Well dug plants have a proper root ball and will adapt quickly to your property.
A huge garden can't be achieved overnight in my opinion. It takes time to plan properly. Acquiring good nursery stock will yield a better result. Gardening on a large scale like you want is not about instant gratification.
If you buy cheaper material that ends up having a 33, 50 or 70% mortality rate two years out, what have you saved when you have to replant?
I would tell her in advance of what you intend to do. She might enjoy the planting and planning.
But honestly do what pleases you but I think half the fun is having a general plant that takes a few years to complete. It grows as you gain experience.