Don't know if this has come up before, but I know that on Style and Beauty a bargain product is always popular.
W7 nail polish. I got it in B&M, two bottles for about £1.80 I think. And I'm pretty sure I have seen it in Poundland.
I am that person who paints their nails and within two hours they are all chipped round the edges. I used this stuff on Saturday evening and my nails are all glossy and shiny and not a chip in sight. It is magic stuff.