You should have taken the $400 a few years ago. No question. For sure. The person that made the offer didn't know what they were doing.
You mentioned a store owner? What kind of store?
I picked up the same model a few months ago for a friend. I think I paid $180 for it. I gave it to him for what I paid. He was looking for a Huebler.
I would guess maybe $250 to $300 on eBay, at best. Maybe less. It's easy to check the sold listings on eBay.
The cue at shown on the original question "Identify Huebler Cue Stick" you posted to is a $100 cue. Maybe 125 or 150 on a really good day.
Huebler prices did go up after he died, but it's the higher models and the Huebler Custom Shop cues that really were most affected.
Right now the price increases you will see in the common catalog Huebler cues are mostly just going to follow inflation, so it's not a true gain in value. The value could in fact go down as the market fluctuates. Certain desirable models do attract better money, and will go up more.
Cool cue. I have several Huebler cues and enjoy them.
I have a Huebler H-14 cue from about 1980. That was the top model in the catalog. I might get $400 - $450 for it with one shaft. But I have three original shafts with mine. One 29 inch and two 31 inch. I also have the original Huebler Deluxe cue case, Huebler joint protectors, and original tags. Hard to say what the whole package would be worth.
I don't know your model number off the top of my head.