How much would it cost to install a new motherboard in a Dell laptop??

I have a Dell Inspiron 9300 and I took it to a computer place that said the motherboard is damaged and needs to be replaced. Just wondering how much that will cost and if I should just get a new computer. The laptop is about 3 years old.How much would it cost to install a new motherboard in a Dell laptop??Probably better to just get a new computer if you can't get a warranty repair.