Need to update my 360... help?

So my 360 got RRoD'd a second time on Thursday, but I managed to get it working again. However, because I don't want to experience these problems again (and I'm very prone to them since my 360 is a pre-July 2007 model), I am thinking of getting a new or used 360 when/if I go the U.S. in December. I could also sell my 360 towards the purchase of a new one. I've got about $300, and that budget could increase or decrease in the future, but regardless, I'll need some money left over to buy Christmas gifts for the folks. So based on what I've seen on sites like GameStop and co., here are my options:--I could get an Xbox 360 arcade system from GameStop and keep my hard drive. I wouldn't have to trade in my old Xbox, but I most likely would, and that would net me about $80 store credit, which would be pretty ideal.--Since I am also looking into getting a larger hard drive, I could also go for the Pro/Premium/whatever it's called, but that's only if my budget allows it. If I traded in my old 360 towards that purchase it just may work. --If I get really lucky, I may be able to find a used Elite or something, which I doubt my budget would allow, but it's a possibility.--I've been considering buying/selling through eBay or Amazon, but doing so (especially used systems) can be tedious. I will look into those options more, though.So, any suggestions? Any help or guidance as to what I should do would be much appreciated. My circumstances: 20GB old model 360, approx. $300 budget, will only be in the U.S. in December), et cetera.