TS-E on the cheap? For architectural photography

You can consider a 400D with 17mm TS-E. Will give you low quality higher ISO, usability problems with tilt judgement. No live view to aid you either.

You can consider a 650D with 17mm TS-E. Will give you much better higher ISO possibilities, a great high res. LCD which swivels (and offere live view) and has a nifty touch interface that you can use or leave, and will give you much better judgement of focus and tilt.

You can consider a 6D with 24mp TS-E II. Will give you a better than the 400D LCD, with live view. Will offer a bigger and brighter view finder, which helps a bit judging focus and tilt too.

You can consider a 6D with Samyang 24mm tilt shift. You get a tad lower quality optics than the Canon powerhouse, less build quality for a lower (more affordable) price.

You can consider a 6D with the old 24mm TS-E, 2nd hand.

This is a fantastically knowledgeable, helpful and clear answer - thank you so much. I hadn't thought of a cheapo new crop body as a clever way to keep costs down but get Live View! Along with Mike CH's observation about the limitations of polarisers at wide angles this is sounding like a great option:

EOS650D+TS-E17mm:

- decent resolution

- good quality Live View for focusing, especially with tilt

- excellent IQ (including avoiding the less good edges of TS-E)

- I don't lose my EF-S standard zoom

From the reviews of the EOS650D it sounds as if I might even be able to get the occasional shot at a quality and resolution needed for a smallish poster-sized print, if I get my technique bang-on.

Any down-sides I'm failing to spot?

Thank you!