I dont know who is charging you $500 to tint a VY sedan (assuming from your 'my ride' is what you got), but that is just highway robbery!
For starters, steer clear of that first link you posted mate. Besides the fact that any film that cheap, will be exactly that (CHEAP!), they obviously have no idea how tint works! They are claiming their 'dark' 75% film is darker than their 35% hahaha
Film readings work by the VLT rating (Visible Light Transmittance) which is the amount of natural light that is able to pass through the window once its been tinted. So the lower the %, the darker the tint is. If they cant understand the simple fundamentals of how the stuff even works, i wouldnt trust their product more than I would trust an epileptic sufferer to hold my nans priceless ming vase! Oh, and the legal limit is 35%.
Ive tinted professionally for over 10 years, and I must admit, ive seen some really dodgy home jobs. BUT, with a lot of patience, attention to detail and persistence, there is no reason why you couldn't do a job that you will be happy with. Having said that, I recommend getting it done by a qualified and experienced tinter. To save the heartache, and if they are good enough and take pride in their work, you will be happy with a flawless job that you know will last a long time.