I use gocollect.com and ebay past sales. I looked a bit more on past sales and you are right. $1900 seems like where this book is. It shot up in value (along with everything else) early this year and has remained stable at $1900 since July.
Gocollect has been having issues lately, I’m about done with that site. The new format is garbage and the values are off as you can see.
I’d caution you to be patient as this hobby is not completely liquid. It is really good, but sales swing between 10-20%. Try comic conventions and haggle with them on the last day. Buying there can save you 12% that the seller does not pay on ebay (your seller really accepted $1672 for this book). Facebook marketplace is becoming an option too.
I obviously agree with you that comic books are a great way to invest. For me, the illiquidity prevents me from over trading and I get some really fun things while it appreciates. I also clean and press books, which adds a bit of craftmanship to the hobby. I pick up low quality keys at comic shops and flip them for 50-100% profit sometimes.
Bronze age should be solid. Get you a nice star wars copy or first Thanos appearance. For me, I think the silver age established icons are risk free. An example is say Silver Surfer #4. Finally, I believe 30 years from now, people will be drooling over the TMMT issues from the 80s.