I can only confirm that. When buying the plants, I eventually stopped keeping track of the costs, but it definitely added up to a high four-figure amount. With a >1000m2 garden, it will surely be five-figure if you don’t only want very young & small plants. Or it becomes just lawn, but then eventually the riding mower will be needed.....
With 1000sqm you only need the riding mower because your wife actually forbids you the toy ;) What exactly have you built into your garden? High four figures (7-8k?) would be more than just a few hundred plants or something very exclusive. As a reference, the range from Hof Berggarten (so rather high quality) where we will probably order quite a lot. There, the perennial bed is about ~10€/sqm, seed mixtures for perennial areas are at most half of that. All in all, I currently calculate about 1000-1500€ for a garden with quite a few plants, seedings, and shrubs. That’s more than the lawn + 3 apple trees + hedge of 10 small bushes garden that was in the calculation, but still not the end of the world. Of course, the shrubs will be rather small, but with 500-1000€ you could easily buy yourself a few years. Moving 5m tall trees isn’t really good for the tree anyway. The only thing that could really get expensive are the flower bulbs. 10-20 pieces/sqm at ~50c each over large areas...