Iphone 6 is much cheaper than 6s. And there is only diffrence of camera and processor version which is not of so much importance because ip6 is sufficient in these two parameters for daily users. other than this there is no major difference between these two.
If I talk about ip6 it uses A-8 chip with 64 bit architecture and M8 motion coprocessor while ip6s uses A9 with 64bit architecture and M9 motion coprocessor. But for daily users A8 chip ( M 8) is sufficient. So without any confusion between these two buy ip6. It will save your money alot without making you suffer from any specification of ip6s.