Dual means you are paying for an instructor to sit next to you.
Solo means you are paying for an instructor to worry about you when you're flying.
Rental is what it costs to hire the aeroplane.
WRT to a school? Bigger is not necessarily better.
If you can, find a school that has done conversions before.
Make sure you get a copy of the syllabus and make sure all items are checked off as completed.
I can't see if you have an IR already, but you may be able to combine some of the flying there.
Note, it's another exam.