The bigger bodied mandolin-family instruments are a niche-within-a-niche. I always say there are 1,000 - 10,000 guitar players for every mandolin player. There are probably 1,000 mandolin players for every mandola, octave mandolin or mandocello player. Mandobass players are never found in captivity. So outside of a place like Carter's, Gruhn's, Gryphon, Elderly, etc. you'll never walk into a shop and find a few different octave mandolins to try out.
So demand for these "big" mando's is small and offerings are subsequently few. In octave mandolins you basically have the A style (Trinity College, Hora, Gold Tone, Weber, custom builders and now Eastman), the F style (Weber and custom builders), and guitar-bodied octave mandolins (GBOM's). The latter include Northfield, some amazing one-man shops (Austin Clark, Andrew Mowry, Fletcher Brock) and a whole bunch of DIY conversions of guitars, specifically older arch top guitars.
There were some pretty forgettable entry level OM's by Johnson, Michael Kelly and similar budget asian imports. I bought one years ago - I still have it but never play it since I got my 21-1/2
Cricket Fiddle (Tom TJ Jessen) F4 style OM. TJ also makes A style and GBOM's. I have no business/financial affiliation, but I really like TJ's instruments and have bought 5 over the years. IMO his OM's sound and play as well as Weber's for less than half the cost. That's why my Michael Kelly OM lives in the closet.
So basically you have the entry level OM's, the Eastman and Gold Tone, some unknown to most but affordable builders like TJ, and then you're in the multi thousand dollar instruments which include Northfield, Weber, Joe Mendel, Clark, Mowry, Brock, Nigel Forster, Graham Macdonald, etc.
Resist the urge to go cheap. The low budget starter models don't sound good, and are nearly impossible to sell for anything but a substantial loss when/if you eventually upgrade. I'd say if experience with the Eastman has you wanting to move up and you don't want to go the guitar conversion route, save up around $ 1,500 - $3,500 for a used Mendel, Petersen, Jessen, Fylde, Forster, etc. (or $ 3,000 to $ 8,000 new) for the next level (Northfield, Weber, custom build). There isn't anything I'm aware of in between.