I got a set locally for my i10......... all I needed to know was if the headlamp was H4, H1 or whatever as most other bulbs seem to be quite generic. i10 is H4, I paid about £6 I think.
Tesco's were dong the sets for about £7 I think, so worth trying the supermarkets. I found Halfords to be a waste of time!
I don't know which headlamp bulb you need for the i20 though, so hopefully someone else will chime in.