Do you think the iPhone 6 may drop in price when the iPhone6SE comes out next month, or do you think it will retain it's price until the iPhone 7 come out in the summer?

The rumoured new iPhone is most likely to replace the 5s as the entry level model, so it's highly unlikely any changes will be made to the pricing of the rest of the range.

The latter....go for an iPhone 6 if you want something a bit cheaper before the 7 comes
out!

I've just bought a 6 on eBay for a lot less than they are new, (I got a 128GB one), it was listed as Grade B but there is only one tiny scuff on the back, and now that I have a case, it looks absolutely brand new! Just an option to consider.