See my reply to Sliwka

Give the grill a once over with a wire brush and then 2 coats of Hammerite. Metal does last longer after this, but does depend on how badly its already rusted.

Cheers!.
I was surprised myself to see the price. Hope it helps.

When I first tried Lidl's Baufix Metal Paint a couple of years ago, I was initially disappointed with it, to the extent that I thought it was a faulty batch. It didn't seem to have much pigment (it was the black version), more like a coloured thin lacquer (Lidl do variously refer to it as a lacquer, even on the receipt). But I soon learned that Baufix Metal Paint needs at least two coats - three or four coats is best. Great stuff when used like that. It is NOT a hammered finish. Bauxfix Metal Paint cannot be compared to smooth or hammered Hammerite, the Baufix is thinner. But it does claim to inhibit existing surface rust. Time will tell. I've even painted the inside and outside of my bird baths to see how it copes immersed in water 24/7. At £4.99 a litre, I would recommend it, with the provisos mentioned above. Better still, for the first coat of paint on any rusted item, I use Hammerite (hammered or smooth version). For the subsequent two or three coats I use Bauxfix. Best of both worlds! Baufix is also available in grey and white.