Generally a four day course and flight test with the CAA. Budget around £5-6k.
Spending on what you want to do with depends on where you start. PPL FE gives you testing privileges for the PPL. CRE will give you the ability to do Class and SPA Type Ratings and IRE. You can hold both and they have some overlapping authority.
Make sure you get them co terminus with your Ground Examiner or you will get stung for an out of cycle revalidation fee!
It is a very challenging course and the test is particularily difficult as you are observing a CAA pilot who naturally flys to an exceptional standard so it makes it hard to pick up on mistakes for the debrief and theass/fail decision.
Before on embarking on it make I would make sure that you can justify the outlay and the recurring costs in terms of return as an Examiner is expensive to maintain especially when you have multiple ratings on it. If you are just looking to regain the R part it will be a very expensive excercise.