Well, even easier then.
You want to order by species rather than by color morph. There are six main species of clownfish:
Percula: The quintessential "Nemo" clownfish. Medium-sized, typical coloration, the default setting of clownfish. Readily available captive bred, start around $20 USD, probably around the same in British pounds.
Ocellaris: Also known as false Percula clowns. They're a little bit smaller and less aggressive than Percula clowns, and probably even more available. Most (but not all) of the designer clowns are Ocellaris clowns. A common variant of these is the Darwin clown, black and white with an orange face. Either variant of Ocellaris is about the same price as a Percula, about $20 or equivalent. If they're just labeled as Ocellaris, they'll be cheap. If they're an Ocellaris but not advertised as such, there's a good chance they'll be significantly more expensive.
Pink Skunk: Among the smallest and most peaceful of the clowns. They don't really come in any fancy color morphs. The tend to be a little more expensive than the base Percula/Ocellaris clowns (about $30-$40), but as there aren't any fancy color schemes they don't get much more expensive than that.
Orange Skunk: Just copy everything I said about Pink Skunks and it applies equally as well here.
Maroon Clownfish: Visually very striking, and absolute hellions of the clownfish world. One of the largest clownfish you can buy, famous for the "lightning" color variant. Very large, very mean. They have been known to draw blood from their keepers. Avoid these unless you have a very large tank or are planning to populate your tank with nothing but bullies.
Tomato Clowns: Take everything I just said about Maroon clowns, but slightly smaller.
If you're just looking for a basic clownfish, any of those species can be had in their basic, wild coloration for between $20-$50. It's only when you start going for patterns that only come from captive breeding (Wyoming White, Platinum, Snowflake, Bullet Hole, Longfin, Lightning, Black Ice, Gladiator, Da Vinci, Misbar, etc.) that you start getting expensive.