I'm thinking of repurposing my 2011 27" iMac as a monitor using Target Display Mode on occasion. I never really had plans to do this, but during the past few months I've gotten 2 more laptops that would work with the iMac as a display, and it could be really handy. The computers I'd like to use are as follows:

• Mid 2011 13" MacBook Air (1.7GHz i5, 4GB, 128GB, macOS Sierra)
• Late 2013 13" Retina MacBook Pro (2.4GHz i5, 8GB, 256GB, macOS Mojave)
• 2017 13" MacBook Pro (2 TB3, 2.3GHz i5, 8GB, 128GB, macOS Mojave)
• Potentially an Early 2011 15" MacBook Pro (2GHz i7, 8GB, 240GB, macOS High Sierra), but I don't know if this computer is ever going to work properly again, so it isn't important.

I know that I would need a Thunderbolt 3 to Thunderbolt 2 adapter for the 2017 MBP, but are there any options cheaper than the official Apple adapter?

And for the Thunderbolt cable itself, are there any good quality alternatives to the Apple official cable that may be cheaper? I'm just trying to save a bit of money as this isn't a setup that I really need, just something that would be nice to have from time to time.

Thanks for any advice.