Most race engine's use a Ti intake and inconel exhaust. For my street engines I use a stainless intake and Ferrea super alloy exhaust valves.
There are turbo engines that run a high quality Ti exhaust valve as well but you have to remember most of these motors are freshened no later than 80-100 passes. I have saw what happens when a Ti valve breaks. IMO it's not worth risking a motor to save a few hundred $$$'s. Some run the Ti valves that come in the S2 heads from the nascar days but it's a grenade with the pin pulled. Todd Humprhies has ran his Ti intake and exhaust valves in his stage 2 heads for the last 2 years in the mid 8's but just replaced them with super alloy. We consider that lucky that nothing bad happened.
Don't cheap out on valves. It's just not worth it. Get a good quality stainless intake and the super alloy exhaust and you'll never have to worry about them.