Ue search- this has been discussed already many times.
Short answer is- P3 on budget is about pointless. Grade to Rec.709 on decent/calibrated display (which cost way less than P3 one) and convert to P3 on export. If you can hire screening room and check how you end result looks like.
There are really no good budget P3 displays and even if you have P3 display this is still far different than grading to projector (borrowed opinion). Grading environment is also very import, e.g. lighting. You can't put your monitor next to window and do your work in nice sunny room
If you really want P3 then I going below e.g. Eizo/NEC level of monitor is really pointless. These are not cheap at all, but still cheap compared to video pro grade 1 monitors.
You definitely want pixel to pixel preview as some edge problems can be "gone" when you watch just downscaled HD preview.
I think you would be way better with renting monitoring than buying it.