I have a exhaust leak on my olds 350?

i have a 77 olds 88 rebuilt 350 rocket and found out it has a exhaust leak. their is a clicking sound when its at normal operating temp but when you first start the car it idles fast which is normaly and theirs no clicking sound you know on some older cars with carbs where when you first start them up they idle fast then give them a little gas to get the idle slow to where it needs to be. well when the idle is where it needs to be at normal operating temp it makes the clicking crackling type noise when your driving down the road but not when you first start it up when the engines at norm temp it clicks. found out it is a exhaust leak the gasket that is between the bottom of the exhaust manifold where the exhaust pipe hooks up to the bottom of the manifold is gone and it does have incorrect exhaust bolts not the normal bolts from what i was told when i had it looked at. i have excellent oil pressure idles at 30 to 40 PSI 50 when you first start it up then goes down to 40 or 30 PSI so its not an engine knock i know with a engine knock you have low oil pressure or no oil pressure at all but this has great oil pressure and is not a knocking engine. exhaust leak is what it is and i need to confirm this also i need to know how much to fix a exhaust leak would be they did not tell me