what would it usually cost to have the struts and shocks lubricated with silicon

Most likely the mechanic means the suspension bushings, but that would not stop a knock, that only helps a squeak, at least in my experience. Why not take your car to a front end specialist and find out the real problem. It sounds like it could be worn strut bearings, worn struts, worn control arm bushings etc. The Honda mechanic should be able to find this stuff, these are not unusual problems. here are some shops: https://repairpal.com/honda-repair-in-century-florida