The wheels on my RX are the heaviest I have experienced and as an old guy with a weak back and a hernia, I don't think I will do this again. To get the wheels back on called for a number of up and down adjustments with my trolley jack, rolling the wheel backwards and forwards until it was in perfect alignment, then laying on my back and thrusting it on with my feet.
I fully appreciate how difficult it can be changing large wheels. I used the same technique to lift the wheel on with my feet. £300 all in actually sounds quite reasonable if you are not capable/confident to tackle such a job.
I admire you guys who do parts of your maintenance yourselves. Alas, I have to pay the going rate. Independent garages are cheaper but you do lose the Relax warranty. Horses for courses, depending on personal finances and mechanical skill.