The link below may help, on mine I simply insert a credit card both sides of the jet and push them in to release the fixing tangs and lift it out, however clips accessed from the other side are mentioned on the IS300 after removing the cover.
There is also a mention of a “check valve” which can result in poor flow.
£122.00 is certainly excessive but we are talking Lexus UK here, Amayama have the genuine articles for around £15.00 a pair shipped.
I did notice there are 3 variants for the jets in the parts list so would assume these are non adjustable for aim?