I am not familiar with the controller market in Asia, so I don't know what is the lowest price. Do you have to actually buy a controller, or just recommend what you would buy?
Normally the choice about the controller would be based on more than just the temperature loop. Typically a boiler has several loops-drum level, feed water flow, steam pressure, etc. One control system, for example a Distributed Control System (DCS), a Programmable Logic Controller (PLC) or a hybrid system would be used to control all of the loops and to allow the operator to start up and shut down the equipment.
If a commercial controller is used, the controller will already have the PID software in it. You will have to supply the gain, integral, and derivative values. These are normally set by tuning the controller during the initial startup of the plant.
I assume that you are to design the PID algorithm as if you were designing a new controller. For simulation purposes, you will need to pick a temperature range. Assume that the output will be from 4 ma to 20 ma. 4 will completely close the valve and 20 will completely open it.