It cost me £1 and took about 5 minutes and I'm going to tell you how.
I have had my desk for around 5 years. My laptop lives on my desk, so it gets used every day but I also use it for painting my nails. I paint my nails almost every day and use acetone on them. I forgot to take a picture, but just imagine... all the finish of the 'wood' has been removed by acetone so it looks like chipboard, with splodges of nail polish all over it. Not nice.
Today I was in Poundland and picked up a pack of 2 plastic place mats for £1.
I cleared my desk and arranged the place mats where I wanted them. The mats are just a little longer than my desk, so I put one mat length ways on my desk. This works great, as the tiny extra length of the mats covers the little gap between the desk and the wall meaning nothing can fall down there any more!
Then I put the second mat width ways at the front of the desk. This leaves a small piece of my desk uncovered at the back, but that's not a problem for me as this is where my laptop sits anyway, so it is never seen.
Finally, I just sellotaped them into place so they don't move around and voila!
Shiny new desk!
If you move things around on your desk a lot double sided tape or glue might be a better option to stick the mats down, but I just plan on working on top of the mats so sellotape should work fine.
And, this plastic should hopefully resist the acetone and not be affected, meaning when I do end up with nail polish all over, it should be easy to remove. :)
Hope this was helpful for somebody!