Give it a go - this link is set up to search for jewellery reduced between 80% and 99% on Amazon.
So, is that a route worth considering if you are looking for a cheap engagement ring, or are the original prices massively inflated?
The first thing to do is to narrow down from the 45,000 results which came up when I searched.
I filtered so it was just showing women's jewellery, and then rings, and then engagement rings. It was still at 1000 results, so I filtered again to those with a diamond gemstone and came up with 98 results.
That's a much more manageable number if we are trying to see if we are getting good value.
I then filtered again to remove anything below £25, as they were clearly synthetic diamonds.
So what was left?
Some of the listings were clearly wrong. I found a 0.16 carat diamond ring for £416, which is an OK price, but the original retail price was listed as £1.49 million, which I would suggest is a little steep - or more likely a mistake. There were loads of listings like this.
However, amongst all those slightly absurd prices there were about a dozen rings which were good value. They probably weren't worth the original retail price but they were certainly worth considering.
There was a half carat diamond ring in an 18 carat setting sold by the Natural Diamond Store Outlet, reduced from £3000 to £600. It was a fairly low grade, but you could easily pay that for a 0.25 carat ring.
The other deal which stood out was a 2.38 carat diamond ring for £2700 by Diamond Jewelry United via Amazon. The original price was listed as £14650. Grading was actually pretty decent with an E-F colour and an SI2 clarity. That price would be it high up in our 2 carat price comparison (top 5 certainly and that's comparing it to smaller carat diamonds).
So, it's certainly worth a look if you don't mind doing a bit of filtering and sorting.
Good luck, I hope she says yes...