Was replacing my brakes and saw this on the front caliper. Mechanic told me I need new calipers for safety reason. Cant that rubber boot be replace by it's own or I need to buy the entire assembly?

 

You can replace just the boot. Make sure you check that the piston still moves freely. If the piston sticks at all, that means there is likely damage, which would require the caliper to be replaced.

 

it’s not require to replace the caliper, that’s just the easiest most expensive option. Your mechanic is a lazy excuse for a mechanic. A real mechanic would suggest the cheaper option of rebuilding the caliper. I highly doubt the caliper housing has any issues at all. Maybe ask him about rebuilding it.

 

Mechanics don't do rebuilds anymore - its cheaper to buy rebuilt calipers.
Do both sides.

Brakes are easy - make some friends and learn how.

 

If the rubber seal is damaged it is likely the internals are damaged water rust heat brakes get very hot.
if you did the brakes yourself the old calipers go back to be rebuilt with a rebate for parts if a shop does the job no rebate on parts.
unfortunately with a shop doing the job you get what they buy.
check rock auto for brake parts there are many levels of quality.
both of my rears froze up completely burned up the pads & one disc.
so yes it is a safety issue as the mechanic has told you.
as rocky said above