Others have touched on the cost of a clean "new" monitor. The question is, "what is your goal here?" Do you just want a nice, better looking monitor in your PP, or do you want to learn and get a better looking monitor in your PP? A corollary: which do you have more of: money or time? Plenty of people are not in a position to learn the ins and outs of repair, no harm or shame in that. In that case, if you have the funds, post a wanted post and get a replacement.
As a basic starting point, you probably want to adjust the monitor settings -- the low contrast may well just be a poorly set monitor.
***Obligatory Safety Note*** Working on a monitor will expose you to 100-150V AC and DC voltages, as well as the high voltages that drive the tube. You don't have to be terrified of these voltages, but do treat them with respect. Don't shove both hands in a powered monitor -- keep one behind you back. Watch where your metal tools go -- a screwdriver slipping can be an "exciting" (and expensive) event.
First, take a picture of the position of all the adjustments so you can get back to your starting point if needed.
There are five adjustments on the neck board and one on the HV section that come into play.
Screen: this is on the HV section and is effectively a global brightness
red drive, green drive: these control how strong red and green are. Blue is the baseline/control.
red/green/blue cutoff: these control the minimum intensity of the respective colors, before it is cut off and becomes black.
From your description of "low contrast", the first thing that comes to mind is the screen adjustment is wrong, resulting in an image that doesn't ever go black -- a blank screen showing a gray instead. This results in a washed out, low contrast image. Again, after noting the original position, rotate the screen adjustment and see if things get better or worse and how they change.
This is the actual process for adjusting the screen and cut offs on a GO7. Do this in low light, with no signal connected to the monitor.
- Set red drive and green drive to their center point.
- Set red/green/blue cutoff and screen to minimum (full counter clockwise)
- Turn up the screen control until the first color starts to show. Note which one as you won't touch it's cutoff in the next step (Let's say it's green that starts to show first, for this example).
- Slowly turn up the other two cutoff adjustments (red and blue in this example) until they just start to show. You should end up with a very faint gray.
Once you reconnect the game signal, you may need to adjust the screen control slightly to get a proper black level -- full black where there is no image.
The above doesn't set the actual white balance -- you need something that can generate a bright white signal -- a signal generator is best, but you can use the cross hatch display in the game test mode, in a pinch.
With a bright white image displayed, adjust the red drive and green drive settings for an even white color. Note that with the cross hatch up, you may get fringes, blooming, or other artifacts that make parts not look white. That gets deeper into monitor maintenance, but in general you are trying to get red green and blue to be the same intensity so that they mix to white.
The one other setting is the focus setting. It does, effectively, what it's name says. It controls the focus of the beams on the screen. If dots are big and fuzzy, adjust the focus knob for best picture.
You may find that some simple adjustments make a huge difference and that was all you really need. It won't fix burn in, but a good picture will make it much less noticeable when you are actually playing the game. You may also find, in trying to adjust the picture, that things don't behave well -- maybe the drive or cutoff settings have zero impact on a color, or setting jump all over the place with very small adjustments, or no matter what you do, things can't be adjusted to proper black and color balance. This points to other problems with the display, that may take much more in depth repair. If the white cross-hatch lines that aren't straight (within reason), or aren't white (you can see individual colors), then that also points to deeper problems.
Your general path to rehabing a monitor (start at the top and proceed until it is "good enough"):
Adjust basic settings (above)
Cap kit and (possibly) replace some or all of the adjustment potentiometers, and sometimes some other parts that should be replaced as part of the cap kit.
Replace anything that dies after the cap kit
Possibly adjust convergence
replace tube
Definitely adjust convergence
Mainly -- don't be afraid to experiment and adjust a little. Yes, you can make it worse -- but if you make it worse and can't get it back to where it was (you took pictures, right?) then there were probably parts that were already failing and it was just a matter of time anyway.