This new idea of yours is a lot more realistic than the new build one, but there is still a major flaw. What's the plan? Hoping that you can get the engine cheap isn't exactly the greatest way of going about things. Take a look at the plans for #503. That's a good start to show the format that you should try to go for.

A restoration of 722 to operating condition would be very much like the effort by TVRM on 630. Massive redo to the running gear, new smoke box, new tender tank/bunker. IIRC the ET&WNC 208 got a significant redo by the Southern before emerging as the Green and Gold Southern 722. That work included a near complete replacement of its fire box and significant replacement of the coal bunker and water cistern around the bunker. The ET&WMC tenders were "cut" down at the bunker for better reverse visibility for the crew. If Great Smokey were to operate her I'm thinking #208 would be appropriate.
As to cost, TVRM's investment in 630 was 650K-ish. Now that work also included making her mainline ready 26L breaks etc. A similar current project scope wise is the FEC #148 4-6-2 being overhauled for US Sugar. The C&NW 1385 is another undergoing a massive redo. In that case we are witnessing a new boiler in addition to a major part by part refurbishment of the running gear. There are good examples for enthusiasts to research to get a feel for what it would take to return 722 to the condition many of us remember her in the 1970s.
It's a loco I'd like to see operate again. 722 is one the 4 from my early youth that stirred my interest in Steam. 630 and 4501 are 2 of them and I enjoy seeing them today. The last is the Ballerina - S&A 750 (FEC 80).

This is all just talk.. but back around 99 when NS donated #630 to TVRM and #722 to GSMR (TVRM never owned #630 until around that time... it was only leased through SOU. / NS.. same with #722 when she ran at TVRM for a bit) I remember some of the TVRM shop guys saying they wished they had gotten #722 because she was in better shape.

I see. Well, to begin with, I've been thinking about what could be done to return the engine to service, and the first thing that came to mind was: Where would it operate? I initially wanted to use a line that runs beside my high school, as it hasn't been used in years. However, it's currently owned by Norfolk Southern and how much it would cross to even lease it and do any nesesary repairs would probably be even more costly than restoring the locomotive itself! But then I thought, Why not send the engine to the North Carolina Transportation Museum in Spencer, NC? The area IS a former Southern Railway Steam Shop, and 722 would be the PERFECT engine to power their on-site train ride! So, it ultimately boils down to 3 options: 1. Keep the Engine at the GSMR and just raise the funds to restore it. 2. Raise funds to buy, transport and restore the locomotive and then donate to NCTM. 3. Buy and Restore the locomotive plus leasing a unused line and extra costs to maintain the mainline.