Tile – Why is wheel oil provided with a Montolit tile cutter

Buy yourself a steel ruler long enough for the job, and a few quick release clamps. Just clamp the ruler and tile to a workbench and score along the ruler with a utility knife. It's a bit slower, but for a single room, the savings is significant.

As well, you should only be cutting the edges that go against the wall. Remove the quarter round and baseboards before you lay the tiles, and reinstall them after you're done. This will cover any imperfections in your edge cuts.

After wasting my money on tile nippers (they don't cut where they are supposed to any better that what you are having, IME) I went the dry diamond blade in an angle grinder route, and short of a wet saw I can't justify, would not do it otherwise. With dust mask and eye & hearing protection, of course; incredibly loud should not be something you experience directly. With a tiny bit of practice it was able to give me excellent results, and I even got to the point where I was mitering wall tiles (redoing an old bathtub with the old tiles needing to be re-used, and no outside-corner pieces available.)

The worst part for my job was cutting very small tiles, but the method I used for that might help depending what your problems with quality of cut are - I had to clamp them in between two boards to hold them steady for a cut and provide a straight edge to follow.

Also the usual "use of an angle grinder generic advice" applies - don't force it, don't let it twist in the cut. Practice on some of your waste tile offcuts.

Alternatively, see about renting a wet saw at the local tool rental place, but if you have a dry diamond blade and an angle grinder, you should not need to, IME.