Have you posted the Dobbs Top Hat in this thread? Please do so if you haven't. I'd love to see it.A good looking, cheap topper would be made from long-nap fur felt and it would have a tastefully formed brim. You're not going to find that new under $450. The only toppers I've seen on the market are made with a crudely rolled brim that emulates a d'Orsay curl. Nobody seems to get the felt surface correct due to the near complete loss of the skill needed to work with long fur (some people use it to make velour hats like the ones from the early 1900s but that's a different skill from the slicked-down fur toppers were originally made with).
You should look on eBay or Facebook Marketplace and hope something comes up. I recommend asking sellers to measure the circumference of hats that don't have a size listed. Sometimes people put hats up for sale that are very large and they don't list a size because they don't realize the whole number with a fraction beside it is a size. You also get the very common instance of people listing the length and width of the head opening. This is very inaccurate but you can measure the length and width of your own hats and see if any toppers match this or exceed it.
There is hope, three years ago I got a Dobbs 7 5/8 silk topper for around $150 in its box. The hat shell is in perfect shape but the sweatband stitching was rotten so I need to re-sew the band in. I also need to re-bind the brim. It's a later hat, probably 1930s or late 1920s, but it has plush on the brim as well as the crown and it looks rather good.
It's worth getting the really large hats that need some minor work. The silk hats are remarkable fixable (cost varies with work needed of course).
The length and breadth measurement is often the best indication of a hat's size. It's not that easy for most people to measure the circumference accurately.
The vast majority of silk Toppers don't have a size tag, so whole number tags or whole number tags with a fraction are very rare.