It seems like you may have underestimated how important having a quality display matters (and how few of them actually exist). That’s understandable — you’d think there’d be better options in the marketplace by now.
Offhand, I see the following optionsL
1. If you’re still in your return window, return the Studio and get an iMac or iMac Pro that suits your needs. It won’t be Apple Silicon, but that may matter less since it’s constantly plugged in and the performance of higher end iMacs is still quite good. Plus, I imagine they’re heavily discounted.
2. Get a Studio Display and don’t look back. Yes, it’s pricey, and yes it’s glorious. I’ve had monitors for 10+ years and even if I only have this for 5 years, it still works out to about 1 US dollar a day (and that’s with the fancy stand). Skip a cup of coffee/tea out every few days and you’ve covered the cost of it.
3. Use what you have and sell/trade in if they ever release a larger iMac that‘s within your price range. Personally, I’m doubtful this is happening anytime soon due to supply chain constrains and economic outlook, both of which make introducing a new premium desktop a risky and costly proposition (especially when they haven’t done the Mac Pro yet).
However, I think they will eventually (2+ years out) release a large iMac and I‘d bet good money it support Target Display Mode. In fact, the Studio Display already does — it ships with an OS (iOS) powered by an Apple Silicon chip (A13 Bionic) and supports another device using it as a display via Thunderbolt. That’s pretty much the definition of Target Display Mode and I’m somewhat surprised (and grateful) that there haven’t been a deluge of clickbaity headlines touting its return.
Should they ever release a large iMac with those capabilities, you might choose to buy the cheapest one possible and just hook your existing Studio up to it. Personally, I opted for scenario 2. I know there are folks who point out that it doesn’t have X or Y, but it’s a surprisingly nice and high quality display and easily the best I’ve ever used. It’s connected to my 16” 2021 MacBook Pro and while that ticks off a lot of the pixel peeper boxes, I prefer my Studio Display for everything from coding to watching movies and playing games.