Lexus keys come in 2 lengths 50 and 55mm if i remember rightly so tbh its really not worth trimming them down for 5mm.
I have provided stav with some keys he's looking at atm as a tester and hopefully he'll let me know if its fallen to pieces etc after a bit of use lol
What you have to realise with the flip keys though is if you want an oem quality one you are going to have to pay for it and more than likely at a main dealer which is going to cost alot.
TBH you should really get charged no more than about £10 for having a key cut you provide, £20ish for one supplied and cut and i have no idea about flips as they would not be stocked and would be special order, but i would think about £25-£30 supplied and cut for a flip or at least thats what i would charge.