IKEA doesn't really do poles to do Bay windows, not any more anyway (only the expensive Kvartal tracking system comes with corners, all the rest are individual straight poles) We do black out curtains though (£34.99 a pair) I work in that department, so know about it from an IKEA POV, but that's it/
Does it have to be curtains though? How about individual blackout blinds, and then have some kind of light decorative curtain over the top?
I'm afraid that I went to a professional curtain fitter and paid loads of money to get a curtain rail (with pullcords) fitted to my bay, because I was also intimidated by the entire concept. (but I'm saving money by making the curtains myself, which is a lot cheaper - if you don't count the cost of having my sewing machine serviced). However, a good DIY book, a drill, the IKEA website and a few deep breaths should supply the necessary equipment to do the job yourself.
For a cheap and cheerful option this curtain pole from B&Q is good, you wont be able to hang really heavy curtains but it will do the job.
Most plastic curtain track will do the job, if you buy it straight you will just need to heat the bit you need to bend with a hairdryer and bend into shape before you fit and make sure you the brackets very well attached to your wall.
If you are feeling really bold you could try fitting plastic corded track (use you hairdryer on the bend again).