Once again I'm thinking of picking up a 6D now that I know that the 7D MKII I was waiting for doesn't fit my needs (a great camera, but I don't shoot fast moving subjects very often). The problem is that most of my lenses are EF-S.
If I wanted to keep my costs down and stick with the body only, I would have a 17-40L (ancient, bought for my 10D before EF-S lenses came out), a 50mm f1.8 MK1, a 100mm f2.8 Macro (non L), and a 70-200 f2.8L IS MKI. The key thing with this combination would be the 17-40 as the standard lens. It is a lot shorter/wider than the 17-55 on my 7D, but the 70-200 becomes a lot more practical at a true 70-200 rather than 110-320 equivalent on my 7D.
Any thoughts?
I stayed away from EF-S lenses completely because I did not want to paint myself into a corner as I upgraded to better camera bodies from my original 10D.
When I posted here to that effect a few years ago, I was ridiculed as being nuts for having such a view. In that day, most people posting in these forums were very reluctant to spend more than the cost of a 1.6x crop sensor body, so most probably never envisioned how full frame sensor bodies would become affordable for them.
My second body was a 1D Mk2N and I've shot 1-series cameras as my main body ever since, going to a 1D4 and 1DX, but I also kept the 10D, and 7D, which I still have although rarely use. I just never really saw any advantage in EF-S lenses either for crop sensor bodies or for full frame because I guess I had the range covered either way with various lenses.
Only you know what works best for you, but I would suggest looking at what you expect your long term path to be in the way of bodies, and begin to adjust your lens collection accordingly.
The 17-40 is an OK lens (I have that one too) and I have been basically happy with it except for softness in the corners. I recently purchased the 16-35 f4, and it is far superior, plus it's image stabilized. If you didn't already have the 17-40 I would advise against getting it. I'll probably put my 17-40 on eBay but I did not want to do it while Canon was running rebates on that lens and others.
I could never be happy with a 6D, due to the crippled auto-focus system compared to what I am used to. But if that works for what you shoot, the image quality is definitely very good. Based on the constraints you mentioned, that might be your best move right now, and it's probably the least expensive upgrade you can make that would increase your overall possibilities.
Good luck.