Differences between Relays

So I'm doing research for my hybrid, Kal-like, HERMS build and I was reading into the use of relays. I understand that by using a rotary switch and a relay, I can completely cut the power to either the whole unit (power switch relay) or the elements themselves (in case the SSR is trying to fire the element when it should be off).

Is there a difference between the big, hulky $30-50 relays like THIS, and a cheaper relay that looks like THIS. And, does anyone know which wires would go where one the second one?

Thanks for everyone's help!!!

Here are some pics of the bulky and cheap below:

On the 5X847 relay you can tell the wiring just by looking at it since it's pretty obvious where the coil and contacts are (IMHO).

On the 1EJG7 relay it looks like the circuit diagram is printed on the unit.

If you don't understand exactly how a relay works and what it does I would suggest a little Googling about relays. I think you'll find the first few articles will explain all your questions about wiring them. They are pretty simple devices and have very little variation other than the number of contacts and their amperage rating.

The only spec difference I see between the two is the contact material. When switching inductive loads (e.g. motors) there can be an arc. When there is an arc there is a degeneration of the contact surface over time that will eventually lead to failure. In heating applications the load is mostly resistive so they're approximately equal.

Even that "cheaper" relay is more expensive than I am used to paying I get them for about 10 dollars shipped. search for "definite purpose contactor". if you are buying a pid from auber instruments you can buy one from them pretty cheap as well.

Thanks guys!