The stationery section of any shop is always worth checking out.
The local $2 shop (Hot Dollar, Woden Plaza) had a packet of 5 pencil grips and umpty ump pencil topper rubbers for ... wait for it ... $2.
The supermarket stopped carrying the pencil grips I've been using for a couple of years so I was very pleased to see these.
Not for use with pencils, obviously, but for knitting.
While this solution doesn't protect the needle tips, it does prevent stitch slippage. These work well on 2.25mm and larger needles. They will stay on the 2mm needles, but not as securely. That's ok, most of the socks I knit are on 2.25mm needles anyway.
The pencil toppers might work as point protectors on larger straights, or perhaps I could join two together with a length of elastic for a combo dpn point protector/stitch holder. Hmm - will get back to you on that.