@Nayxx how many k's has the car done and has it been serviced according to manufacturers date/time schedule its whole life?
If so, the other avenue is to look at your Consumer Law statutory warranty claim as lifters/cams shoudln't go titts up after just 11 years (if it's a low mileage example of an 09 VE)...
I'd also, clarify exactly what the mecahnic actually meant as it could be that he quoted for only lifters @ $3500 but felt it was not the best option to take as the cam was also likely stuffed AND unless you addressed the cam at the same time, then you'd soon be back having to replace the lifters and cam @$4500 (to correctly fix all damaged parts, including the newly installed lifters)... do it right the first time may? have been what he was trying to get across... So clarify exatly what he ment and what guarantee he would provide on the engine and workmanship.
Others can mention how much engine work is really needed to be done if lifters are squeeking (guess it depends on whether metalic particles are going through the oiling system).
Also consider going back to the mechanic that did your oil change (if you suspect the wrong oil was put in it) and have an oil flush additive put in, run the engine for 15m then dump the oil and filter and replace with new (correct grade) oil and filter ... but such is a long shot as squeeks as metal on metal sort of noise