Ring and get a price, Lexus do a fixed price service for cars over 3 years old, which is quite reasonable. Mine is due a minor service next time around, which is £159 - considering that they use 6 litres Shell Helix Ultra Extra and a genuine fuel filter, the parts alone are probably £75, I dont think thats bad.
On the other hand, at 3 years and 31k miles, it couldnt need much - probably just an oil and filter change (check manual - i dont think the fuel filter is due until 4 years/40k miles). If you wanted to go the indie route, you could probably get 6 litres of Comma Pro-Tech 5w30 C2 oil for around £30 and an adl blueprint oil filter for the £6 mark. Bluerprint fuel filter should be under a tenner if you wanted to get that done too. Probably get it all done for £80-90.