We know that SH Figuarts have a 1/12 General Grievous in the works having had it turn up at one Trade Show last year. What we didn't see coming was Bandai releasing the General first in their 1/12 action figure kit line.
As seen here on Tag Hobby, the 1/12 Greivous kit will include all four light sabers. It also has options to display him with two arms, or with the arms split into the four armed version. There is also a cape which looks removable.
Greivous will be released July 2017 and the Japanese RRP is 4500 Yen. That is £32, but bear in mind that the licence agreement wot allow these to be sold outside of Japan. That means you will have to rely on a import at a premium price.