Lead valley replacement

As part of our front porch replacement which is under the front part of our bungalow roof, we have a lead valley that has seen better days, depending on which was the wind/rain blows, it leaks through into the porch.

This is the only valley on the roof, so matching to other valleys isn't an issue, but would there be any particular reason to opt for a GRP/dry set up over a lead/wet valley, and would there be much costs difference between to two?

At present our roof has interlocking tiles [Redland 49] and no felt. Would I expect a membrane to be fitted around they valley as part of this work?

Thanks

a preformed grp valley trough is fine on 49s.
a big cost saving to be had.

That's good too hear. Is there any merit to an open valley over the ones that have a central upstand?
We don't have any trees that would shed leaves into gutters etc if that is a consideration

Personally I use an open valley pointed..
but thats my choice. its slightly more work.