A while ago my grandmother was cleaning out some of her jewellery and was going to get rid of a lot of it since much of it was broken etc. She let me go through it and take any pieces I desired. One such piece was a thick banded silver ring that was quite tarnished. I was unable to remove the tarnish (in most of the places it was simply just where the paint had come off) but still wanted to keep the ring, so I decided to give it a new lease on life.
As I already had the components at home, this didn't cost me anything. Many people would have access to nail polish (whether their own or a friends) if they do not wish to buy it. If you desire a cheap ring to try this out on I suggest trying your local thrift store.
Timewise this shouldn't take any more then 30 minutes, it depends on how long the nail polish takes to dry / how many coats you give it.
This is the ring in question. It's quite smooth and very plain. A more detailed ring would also work however would require more care to be taken with it.
Select the colour nail polish that you wish to paint your ring. All that you have to do is apply smooth strokes of nail polish over the ring ensuring that you don't get any bubbles / lumps etc.
You will need to apply more then one coat, particularly if you want a more intense colour and also so you can't see the metal through the nail polish.
I found mine dried really fast (and I didn't use fast-drying nail polish) so I applied about 3 coats to it, letting it dry on newspaper inbetween. Make sure you remember to paint the inside and the edges as well.
Once everything is dry you can either stop here or give the ring a coat of clear nail polish. This will give the ring a more shiny appearance (if that's what you desire) and should give it a bit of extra protection.
You could also possibly achieve this with a mixture of PVA glue & water, but don't quote me one that.
I think the best thing about this ring is that if you grow tired of the current colour you can just simply use nail polish remover to strip it and start again!