You will need some knowledge on relay logic concepts, lots of enthusiasm, a PC and a PLC software, preferably with a simulator to simulate your logic, and of course time to browse the internet/ read and understand PLC related forums/ website
Your least expensive alternative is probably going to be AutomationDirect.com. They have a DL-05 unit for arounf $100, $100, and a cable for $30.00. I suggest you add an analog card to explore working with anaolg systems, and that is $80.00.
Other brands have starter kits, although these may be a little more expensive. GE VersaMAx micro and Allen Bradley's Micrologix 1000 are good starters. If you contact your local distributor you can get pricing.
Hai Misurati.
Bacically you will need some knoeledge on relay/timer logic.If you are having PC with internet connection,you download the picosoft3.0 free software from the www.ab.com/plclogic/pico web site,and setup your PC.In this software the simulation tool is available,It's very useful for develop your plc program logic knowledge.Try to use it.
Best Wishes,
S Shanmugam.