18 month old laptop basically irreparable

I purchased a Dell Inspiron i5 3521 from Makro in November 2013. The machine has been in normal daily use, until 2 weeks ago when we were suddenly unable to boot it up. I took it to Ensure IT Services (Pty) Ltd (a Dell authorised agent) in Ndabeni who have quoted me R8070.99 to replace the main board. The actual cost of the main board itself is quoted at R6779.82! The entire machine cost me around R5200 brand new 18 months ago. How is this possible? a quick trawl through the web shows motherboards for these machines quoted at between $200 and $400 on several American sites. I am extremely irritated that a) the machine has failed badly when barely out of warranty, b) the warranty period is so short as to be almost useless, and c) I have been quoted a ridiculous amount by a Dell authorised service centre. I will be taking the machine to an \independent"repair facility to see if I can actually get it repaired for a realistic price (in my mind that would be less than half of what it cost to buy new). Needless to say"