If you want/need to try it on the cheap, phone Wirral Spares 0151 651 2228 (borough Road Birkenhead), if its an expensive screen he might be able to supply a secondhand screen but will also quote for a new one and he'll give you a number for a screen fitter.
So I'd be buying the screen from Wirral Spares and paying fitter separately?
If your excess is only £50 then that is the way to go, if its around the £100 then it might be worth shopping around unless its a special screen such as a heated one @Excoriator mentioned above. Don't forget that glass claims don't normally affect your no-claims bonus.
My excess is £100 and NCD not affected, but some insurers (I don't know if that includes esure who I'm with) include glass claims in their premium rating and claims need to be declared for 3 or 5 years depending on insurer. If I can get a screen for not too much above £100 I'm tempted not to go through insurance. Screen isn't heated but does have headlight/wipers sensor. (Citroen C5)
Autoglass's book prices for non-insurance jobs are stupidly high
They're quoting £424
but they sometimes negotiate face to face if they aren't too busy.
How does that work? You haggle with the fitter?