Cheap DSLR body with a great lenses , will the photo still be great?

80% of what goes into making great photos happens outside of the camera. Having a $50,000 camera and no idea what you are doing will only result in bad photos that are super sharp.

Agree with others that you should put more money in lenses than the body. A cheap body with a great lens will always produce better looking photos than a expensive body with a cheap kit lens.

Since you want to do video, I would recommend that you stick with Canon over any other brand of DSLR. The only thing better than Canon for video is Sony or Panasonic mirrorless cameras. Both Sony and Panasonic are many years ahead of Canon in terms of their video performance. The GH4, which was discontinued last year, is still much better at video than anything from Canon at any price.

You should also understand what are the pitfalls of using a DSLR for video. For example, you can't record longer than about 12 minutes in full HD because the camera can not record files larger than 4GB, which is about 12 minutes of 1080p video. Making too many back-to-back videos will cause the camera to overheat and will result in shortening the life of the camera. When in video mode, instead of useing the entire 18MP sensor and then down sampling the data to the 2.1MP 1080p format, the T3i will only use the center 2MP of the chip which means that you will have an additional 3x crop factor on top of its already 1.6x crop factor. So if you're looking to do wide-angle video shots, you won't be able to do it with a DSLR like the T3.

I would strongly recommend that you consider a better T series or, if video really isn't all that important to you, go with a used Pentax K-50 or a new K-70. Both are significantly better than any entry-level DSLR from Canon or Nikon.

You will get "great" results only if you know enough about what you are doing.

Better lenses can help up only to the point where a cheap camera

can't properly resolve what is coming through them.

I would want Both a decent camera body And a good lens.

When it comes to "where do I spend most of my money", I go with glass every time. Unless you're blowing up prints to mural size, better glass will get you the pictures you want long before a high megapixel full frame camera. That being said, I don't recommend buying way-out-of-date hardware. T3i is ancient, in camera terms. I currently rock the T5i, but am looking to upgrade. If I was brand new to buying, I would recommend the T6i, T6s, or T7i. The 24mp sensor is a good step up from the 18mp in previous generations, and the feature set alone is worth the money. If cost is an issue, Sams Club usually has T6i kits on sale for a real good deal. Sell off the kit lenses for cheap and put the money towards real glass.

Glass I currently own:

70-200 f2.8 L IS II

400mm f5.6 L

10-22 f3.5-4.6 (if you've never owned a super-wide, GET ONE. Tilt shift is even better but more $)

18-55 kit lens. Never use it.

Also own a 2x teleconverter. The 70-200 f2.8 becomes a 140-400 f5.6, which on an APS-C camera, comes out to like, 224-640mm @ f5.6! Having an image-stabilized 224-640mm zoom lens, and still with 5.6 worth of aperture, well worth the price of admission I promise you. I also use the 2x on the 400mm f5.6 prime to hit 1280mm (400x2*1.6) which is amazing for eclipse photography. I can also use it to easily track sunspot progression, which is impressive at this budgetary level.

Looking to pick up the 24-70 f2.8 to fill the gap and allow me to ditch my kit lens completely.

If you know what you're doing, you can just about get away with any kit, but DSLRs' video capability is more of a selling point than an actual ability.

The 600D isn’t great at higher ISO but I have used one for a number of years and it can take great photos.

Just beware that canon EF lenses are better on full frame bodies than crop sensor bodies, but that is the nature of optics. There are some very good EF-S lenses, see for example

https://www.the-digital-picture.com/Canon-Lenses/C...

I have an EOS 400D (aka Rebel XTi) that is 3 generations older than the T3i - it still takes great photos!

I also have an EOS 450D (aka Rebel XSi) that is 2 generations older than the T3i that also still takes great photos though the shutter release button is a little temperamental!!

As you correctly state, lenses are more important than camera body for good image quality. The lenses I use most are EF-S 24mm f/2.8, EF 40mm f/2.8, EF-S 15-85mm f/3.5-5.6 IS and EF 70-300mm f/4-5.6 IS

It should be with great lenses