all valid points and probably all from experience. I too have done the "budget" build and ended up spending more $ than several new good quality rifles on the market today and does it shoot any better??
This all depends on your intentions, what are you really hoping for in the end? how much shooting will you be actually doing? What distances and what is in you mind, your "budget"?
Why a 458? nothing against it, just asking.
instead of spending $ on one of the 4 you listed for the build, consider what you really are willing to spend and search the options from there. Say if you think you will spend $800 on this build, look at what can be purchased for $800, just as an example.
I personally have a couple Marlins, a RAR and have shot the savage. All are very good shooters for $300 ish/ Are they long ranger shooters, no but they get the job done under 400 yrds. I have no experience with the 783 but as mentioned it is a clone of the X7, when Rem bought Marlin, Rem discontinued the X7 line and introduced the 783 to replace the *** 770 as Rems entry rifle.
If you want to get started shooting, purchase any one of the 4, shoot it until you have $ saved to get what you really want then sell it for almost what you initially paid.
Just my thoughts on this matter (from experience)