I think it helps to point out the technical differences between big TV screens and computer monitors. This also explains why the price is different.

Screen size alone isn't what makes up a good screen.
We forgot to mention one vital value called dots per inch,
dpi. It defines how many pixels (dots)
per inch make up the actual picture. Ever looked at the Apple 'retina' displays or the latest mobile phones with dpi in the 400+ ranges? Looks pretty sharp, huh? Well, it is

and that's what makes it more expensive (among other things). For instance, the latest 4.7 or 5 inch mobile screens incorporate a resolution of 'full HD', which is the same as a 40 inch TV screen may give you, on a much smaller area. Same goes for computer monitors in another quotient though.
So the difference is the area at which those pixels generate the picture, leading to a sharp impression, or not. Does that mean that a modern TV screen isn't sharp? No, but it's way less sharp than a 24-27 inch computer monitor or the mentioned mobile screens with the same display resolution.
This doesn't harm the impression when watching TV, fast images, movement, scenery, but you will see a lot of difference when working with text or gauges. Again, the TV isn't unsharp but it's worlds apart from working on a proper computer monitor. To get rid of this downside, you would have to step away (literally) from the 'low-res' TV screen, which then causes the big picture to become smaller in comparison. You don't sit directly in front of a 40 inch screen, do you?
Therefore, a big screen is just one part of the puzzle when it comes to displaying information. Reading text, gauges and documents of all kind are better off with a computer screen, while the big sport events, films or videos of course come in nicely on large screen setups. For those things, even high-res beamers may be great and worth a shot. Getting really big!

The bigger the screen gets (while the resolution stays the same) the lower the dpi will get as less pixels per inch will cover the actual screen area. Take an average 24 inch monitor supporting full HD, 1920*1200 resolutions. It will give you 'sharp' ~95dpi while a TV screen with 40 inch and the same resolution only offers 57dpi.
That's a 40% loss in sharpness.

By the way, this may explain why the TV and home cinema folks now head for the so called
4K standard, offering higher resolutions on big screens, therefore getting rid of the low dpi problem.
To conclude, the sharpest and biggest you may currently get are the 27 inch (sometimes 30) computer monitors offering resolutions up to 2560x1440. A 30 inch screen then comes in at ~98dpi, so it's as sharp as a smaller 24 inch monitor with 1920x1200 resolution. And, that much is true, those screens aren't really cheap.