Hey guys, what are the signs of blown Gasket and how much it cost to replace it, is it possible to do it myself?

 

do mean blown head gasket? some signs for that are yellowish oil (from coolant getting in engine oil), smoke from exhaust, low coolant without an external leak, etc. This is a big job and might reach 4digits$$ at a mechanic . If you mean valve cover gasket, oil pan gasket, the signs are oil leaking from the valve covers or oil pan. This you could probably easily do yourself.