Low priced universal USB ARM JTAG that works with a broad range of devices and SDK's?
Ouch - difficult question, and one I know a lot of folk would like a good solution to. I use ARM and FPGAs a lot, so I'd love to have something reliable to use that works with more than one vendors chips.  

I looked into this a fair bit a while back, and found OpenODC, and stuff like the Wiggler and the Amontec JTAG Keys, but you will have to do quite a bit of work to get it all set up, and of course it being reliable, easy to use and bug free is unlikely.  

Like any free or open source path, sometimes it's the way to go (e.g. if a project is mature - I use Kicad now for PCB development and find it just as good as the commercial options I used to use in the past) but sometimes it's just not worth it, you have to figure if your time spent setting up and battling bugs, etc is worth the savings in the end (which is hard to know before you begin)
From what I have seen, I made the choice to go commercial pretty quickly, as I don't think the open source JTAG solutions are mature enough yet to bother with if you are developing professionally. I may be wrong though, and in any case it's certainly worth a couple of hours Googling to figure it out for yourself.