Thanks for the reply! My electricity is currently at $0.06/KWh (Price in USD)
Assuming that is with taxes that is quite good. Can I ask location? (not anything like address just like state or country if out of US)
With that you are lucky as you can go into previous gen's. I would say anything S3 and up. (I suggest getting the S3+ if you go that route as it normally is not much higher for a better unit). You can get these off ebay.
If you don't have PSU's keep in mind you need to buy a psu. Also summer is coming so I suggest starting slow and building up if you want more. Work on exhaust and find a good way before throwing a lot of cash in.
If you want pretty much most efficient chips then look at S5, SP20, Avalon 4.1.
You can do exact calculations here:
https://bitcoinwisdom.com/bitcoin/calculator