In a lot of countries, getting a Vita has become pretty cheap thanks to the Playstation TV. The bundle was $50 in the US and $60 in Canada just recently and that included enough memory (8GB) to play SAO and also a controller. Made me pick up one. Not saying it's an option for everyone but it might be worth keeping your eyes open for deals on the PS TV model if you only want the Vita for one game. I think the Vita has been building a pretty decent-looking library so I'll get some more games too eventually.
Thats an interesting option, Amazon UK listing it as £45 for a PSTV though it doesnt mention 8GB memory and says controller isnt included in this case. Does the PSTV have 8GB internal or did the bundles just include a 8GB memory card. I have a spare DS3 controller from my PS3 that never gets used so that could be an option for me. Having to use the TV for it is a bit of a hassle considering I already spend a lot of time on PC and handhelds are usually a break from that but this seems like a pretty decent alternative to buying a vita.