Cost my son over £600 for his old Clio and I was quoted £900 for my Megane which I declined and got different car. May depend on part of country you live in for labour costs.
^ Yes do not get it done at a Honda dealer. If you do want it done go to a good small independent garage. It would be worthwhile getting a decent mechanic to look at it, they will be able to give you an idea if it is just a blown gasket or cylinder head damage. It it's head damage then buying another car on part exchange may be the cheaper option.
Was there any history of overheating?