I'm not a gardener who normally grows a great deal of dahlias, maybe one or two a season, but last summer I grew about 100 for flowers for my daughter's wedding. So I had to learn fast and did lots of reading! One tip I found and used was to use tomato cages, but cut the legs off and put them upside down over the dahlia plant, so it was like a cone over it. I then used landscape staples to anchor the cages. I did have to, later in the season, add a stake to stabilize a few cages, but being that the dahlias were in a cutting garden I wasn't overly concerned with aesthetics. Conversely, the few that I planted out in the regular perennial gardens didn't need as much support due to the fact that I had no choice but to squeeze them in where I could find room and had help from neighboring plants! On some of these I simply used a (shorter) stake and then tied the dahlia to it loosely with twine.

I decided to overwinter the tubers (more research and learning!) and despite losing quite a few, I have again well over a hundred this spring! I intend on using the upside-down tomato cages again in the cutting garden, since they worked fairly well for me. If your blooms are as heavy as you say, though, I wonder if the tomato cages will work? They are, after all, IMO, a bit flimsy. Plus, I cut most of my blooms to either use or to promote continued blooming in time for the wedding. That probably helped to lessen the weight.

Good luck!
:)
Dee