We had ours replaced by Gary at COVERIT. It probably wasn't the cheapest, to be fair we didn't shop around, just went on recommendation. We also had a complete new frame. It was £900 all in and was done from start to finish in 2 days. Ours wasn't a standard fit either as our windscreen has at sometime in the past been changed from the standard Norman 23. Can't praise them highly enough. It really is a superb job and totally changes the stern of the boat.
Although Coverit do a superb job, I have used them in the past,try asking at your local Marina, other boaters and look on ebay boats for sale. It is a lot of money so worthwhile looking around.