£14K for solid timber triple glazed is £1400 a piece for 10 units.
You are calling the ‘casement’ windows. Are they all openable or are some of them fixed lights? Fixed lights are cheaper than openable windows because openable windows have an outer frame, and inner frame, the ironmongary, and all the gasketry.
If that’s an installed price, it seems like a pretty fair price for solid timber triple glazing.
Don’t pay extra for argon filled cavities, it’s sold as better thermal performance and it works when tested, but the argon will not be in the cavity in the glass 2 years down the line. It will have bled out through the silicone seal.
In regard to sound attenuation, you’ll notice the difference with triple glazing, but you’ll also get a less light in your rooms because the frames are chunkier, and deeper, and the corners will look bigger where the windows meet as they facet around the curve.
Additional sound reduction as you refer to it, when done right is additional rubber flipper gaskets in the glazing channels that hamper sound trying to bypass the glass, and if you are buying aluminium clad timber windows, a little rubber pad between the aluminium fascia and the timber frame.
My gut instinct is that £14K ballpark for fitting two 5 panel casement windows is a fair price. You may be able to approach a glazier on your local Facebook page for your area and get a better deal, but you won’t have a known name who has a reputation to protect and won’t want to be talked about online.
If you can shave a couple of grand off that price, then maybe take the chance, but I’d stick to Anglian if you’re talking about less than a 10% price difference. But that’s just me.