I was brief before sorry RedPencilPot.
For example the similar ring here is the same gold, same colour diamonds, but a slightly better quality (SI is slight inclusions. VS2 is veryslight inclusions)
www.justeternityrings.co.uk/eternity-rings-half/18ct-yellow-gold-half-eternity-rings/jew085y-18ct-yellow-gold-ring-with-15-channel-set-princess-cut-diamonds-and-36-round-diamonds.html
and it's £1,300 less.
If you order online you have a 30 day money back guarantee from these kind of suppliers, I think that's because of distance selling regulations? All you lose is the cost of safe postage for a return.
If you go to the high street and try on some styles then shop around online you should get a feel for the kind of price the ring you want will cost, or alternatively see what you can get for your budget.
In the past I've had one off jewellery designed and made for me (two rings) and also been to the jewellery quarter for an appointment and chosen stones which I had set into a standard setting. The stones came with certificates of authenticity saying exactly what they are.
It was a nice experience, chatting first with someone, explaining what I wanted and then going in by appointment. Not everywhere has a store front, my appointment was in an office suite where they'd got the stones in for me to see and where we looked at sketches and designs and I tried a few things on before deciding.
Here's a link that explains how prices are affected by the size of the diamond(s) the cut, how the craftsman has made the best of the stone and the expertise in cutting it which affects the 'sparkle' the colour, which is the natural 'brightness' for white diamonds and also the clarity, which is the natural specs or errors in the stone. Lots of stones that add up to say a carat or more, cost less than larger stones. Benchmarks are the full and half carat sizes where cost goes up significantly more than say 0.48 or 1.03.
www.adiamondbuyingguide.com/diamondprices.html
Hope all that helps, the links are selected at random, you can find absolutely loads of sites on line and whatever they call themselves for trading purposes, they do tell you who the business is owned by. Have fun looking.