It's safe to say, "Invest" 1st in your subscription for three[3] consecutive months of FFXIV(both of you) and worry about the extra PC/PS3 platform later. If you don't want to be left out of the Legacy program, I think you deserve that much if you stuck with the joys/pains SE has given you through the game(lol). I think it's a good deal (business, economic wise and socially).

I planned the build of my PC way before FFXIV beta but I also have a PS3 with 250GB of space, so that's ready too. I'm not rich or have a high income. You just need to manage and be responsible and everything will go peachy. I know by the time your ready, the build of a new PC or getting a PS3 won't be so stressful but worth it cus you'll be a Legacy player!

Good luck!