I wanted to learn about PLCs recently, there are loads of resources available on the internet some with PLC simulators.
I bought a secondhand PLC off ebay and learnt basi ladder logic etc by experimenting.
If you decide to buy one (and I reckon it's the best way of learning) make sure that you either get the software with it or that the software is available free.
Some makes of PLC charge a fortune for their software others let you download it FOC.