It seems a bit expensive to go to programmable logic, when you have a computer sat there, which, while the PLC is working, will be sat doing nothing. The problem with programable logic chips is you are programming in machine code and, unless you have the development tools, you will have to buy those as well.
You can get a download from Microchip, which emulates their chips and allows you to write programs, but then yo need the hardware to program the chip.
I would have though it would be just as easy to get another port for the PC and use that. Programming can be using Visual Basic.
Looking at the diagram you downloaded - do you need a wire to each station - or can you put a binary signal to a group of wires - which selects the staion you want.
That doesn't matter a great deal, however. The thing to do is identify all the outputs you require and build the interfaces, particularly those to control the three phase motor, and the relays or whatever for the various locks.
The logic to control it would, I think, be fairly simple at the side of that.