Howdy. After extensive research, there are 3 that I'd recommend, depending on your budget.
The first is the Igloo Cat Carrier, which is about £16.99. Good quality but inexpensive. Try doing a uk google search for "igloo cat carrier".
The second is the Gulliver, which is around £21.99 but is more spacious and more solid.
And the third is the Cargo Cabrio Cat Carrier, which is normally £29.99. Bit of a mouthful, but it's a fantastic carrier that opens up at the top as well as the front, has a shoulder strap as well as handles, and even has bowls integrated into it! Great piece of kit if your budget will stretch that far.
Whatever you go for, though, bear in mind that you're only going to buy a carrier once in a number of years. And I say that from personal experience. No point in spending as little as possible for something that won't last as you'll end up spending more in the long run. That said, some people seem to get by using cardboard ones, though I wouldn't recommend it. I have just this minute returned from a trip to the vet to get Lilly snipped 'n' chipped, and I'll tell you what, I am SO thankful I spent a little more on the carrier when I did! It's traumatic enough for her and for me without having the hassle of a carrier that's not up to the job.
Anyway, hope that helps. Please ask if you want more info.