what must be done to an e eseries head to fit larger valves

Pull the head off, port the head, flow the head, match port to intake manifold choose oversize valves, may as well put in valve springs good for 600 thou lift to take advantage of the head and a good cam to use the additional air/fuel mix, bump up the compression if you are staying normally aspirated.

Kiss $1500 to $2200 goodbye, honestly not good value for $$ when you weigh it up for Rwkw, but it will bump it up with the right cam, you may need an aftermarket interceptor or Aftermarket ECU to take advantage of the cam and a retune.

It really depends on how big you want. You cant go much bigger than XR size valves before you run into problems.

To fit XR or slightly oversize valves to a std head will be somewhere around the $400-500 mark. You would probably want to recon the head, clean up the ports, mill it flat, weld up any corrosion, fit some tougher springs etc you would be looking at somewhere around $1000-1500 depending where you go and what you get.