Click is about as cheap as they come, and as far as entry-level PLC's go, probably the best on the market IMO. But they are limited in what they can do.
A micrologix 1100 is a great middle-ground, as you can get free software for it, and it has onboard ethernet. If your plant is primarily AB, this is a good option.
If your plant is primarily Siemens, an S7-1200 is a good middle-ground controller, although I'm not sure about software cost.
If your plant is primarily AB and you have a little more money to throw around, a 1769_L16 CompactLogix is far and away your best option. Not overly expensive for what it is, and it's latest-generation stuff with the latest programming environment. But speaking of the programming environment, the software is not cheap.
My 2c would be, start with a base model Click. It's a very small investment and will give you a reasonable starting point. If you find you like it and want to go further, consider a ML1100 or a S7-1200, depending on what you have most exposure to. If you play with the click and find you love it, and definitely want to get into this, I'd go all in and make the investment in a 1769-L16 CompactLogix and the software. Well worth it, if you want to give yourself real-worl experience.