Check the coolant level. Ensure the coolant hoses to the IAC are not clogged. Have the IAC cleaned.

Blue smoke from exhaust is an indication of oil consumption and replcing the valve seals would reduce at least 60 % of the smoke. The ideal way is to replace the piston rings as well.

As to the knocking noise, it would depend on if it is the top or bottom section of engine that is emitting the noise.

Cost would depend on how you want it to be done. You can still use the engine for the time being if you don't widh to do any repairs but if it is the bearings that are causing the noise, that should be the ones you need to look at first, which is critical and can result in engine failure if not atytanded to. Have a second opinion on that but low oil level can cause such faults.