Looking to increase my iMac's RAM

The official RAM specifications are given by Apple here: https://support.apple.com/en-us/HT201191

Using the list, you need to

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

• PC3-12800
• Unbuffered
• Nonparity
• 204-pin
• 1600MHz DDR3 SDRAM

Note that only 32 GB of RAM is officially supported.

http://www.crucial.com is a great website for checking RAM and other hardware compatibility. They also have a scanner tool (http://www.crucial.com/usa/en/systemscanner) to detect your computer type and give you a list of hardware that will work with your computer. Generally, they offer competitive prices.

Note: This is not promotional just trying to provide one of the best sites I have found. I am in no way affiliated with the website. The part about

Generally, they offer competitive prices.

is not promotional because the OP said

If I could find a better price, it would be amazing.

and therefore was looking for a "better price".