Personally, I would prefer Barlow come in and sing everything he's not on, EXCEPT the Stu albums. This would clearly define two separate eras of Iced Earth. I came in late to Iced Earth. And while the first guy was OK, and Ripper was OK, Barlow is THE BARLOW, and given that he already did Days of Purgatory, I don't see the problem in him re-recording the early albums entirely again. And I like Ripper, but I think Matt has a more commanding voice.
As for costs, they are at Jon's studio, so all the overhead would be whatever they already have. The costs would be associated with the personnel involved engineer, mixer, mastering), the cost of having the band flown in and paying for their food and lodging (which can get expensive), and then ultimately, you then have to see how you want to release everything. Would not make sense for digital-only. Do it all, or don't do it, in terms of physical and digital. My guess is, if they do it, you do it under your own label, and sign a distribution deal with a major label. This way everything is under Jon's control.
But whether I purchase would really depend on who is singing. I have the catalog, so if it is just re-doing the records with the same singers, then no. If it's re-recording the first couple, plus the Ripper stuff, with Matt, I'll buy them.
If it is Stu (who I personally really enjoy) doing all of it, then absolutely not. I love his era, but Barlow should never be recorded over. Ever.