This appears to be a common problem click here.
Epson, along with other printer manufacturers have a policy of selling the printers cheap and then charging exorbitant prices for parts and consumables. If you don't really need the LCD but can't use the printer without it, then your best bet might be to scrap the RX600 and buy a simpler printer.
The Sale of Goods Act click here is on your side because 18 months is not a reasonable time for such a major failure, and your case would be against the retailer, but I doubt that you will get very far. You could try opening a thread on this subject in the Consumerwatch forum.