Hi Anthony,
I had the same issue with my GT which has different size blades and the large one was £130 alone.
These are old style wiper blades and not modern flex blades, so I found a site that does replacement blade inserts, so as long as the blade holder is sound you can remove the rubber blade and metal inserts, cut new blade to size replace inserts and thread back in.
Mine came with 4 rubber blades for about £25, so enough for two sets.
If you have trouble finding a site let me know and I will look up where I got mine from.
regards Eric