As you can see from my handle, I LOVE my 444. It was the last gun my dad bought for me as a kid, before I was responsible for buying my own. It's an older model and the 265gr flat point from Hornady shoots around 1" when I do my part. I'd say a 444 is definitely worth $400, regardless of manufacture (Remlin or Marlin) and if it's a JM stamped Marlin 444ss, it's worth way more than $400.
It's a capable round, for sure, and it depends on whether you want to have a turnkey big bore for 300gr+ bullets, or if you want to reload to get the most potential.
I'd say if you want a turnkey rig, a 45-70 would be an easier solution with readily available loads of 300-400gr.
If you want to handload and take advantage of higher sectional density and a little more exclusivity, go with the 444. (And if you don't reload, there are 300+gr loads out there, but you'll pay $$$ for them.) If it's an older model with microgroove rifling, it *might* have issues shooting the 300gr loads well, and might need tweaking to do so. I stick with loads under 300gr since they shoot so well, and offer pretty decent trajectory, so I don't have good advice for 300gr+.