Trespass are fine. To be honest, I do not think there is that much difference paying £50 or £100 for a jacket. They will all be waterproof but that is about it. As long as you are sticking to the piste and not heading up a glacier it will be fine. I would consider buying trousers as well. they can be had for £30 in some retailers and the cost of hiring will be nearly as much.
Just did a bit of googling for you there are some bargains out there!
http://www.mandmdirect.com/ProductList.asp?Filter=1|Mens|3|Ski Shop&a=resetsearch
You can get fully kitted for much less than £100!
In regards to goggles, I would just borrow some, though would recommend buying some. Only old farts wear glasses on the slopes. Goggles all the way. I am really fussy with my goggles as rubbish ones can steam up and can have terrible lenses / field of vision. Problem is, a decent pair is well in excess of £100.00. My Oakley A-Frame Iriduims cost me £130.00 but have lasted for 7 seasons now and are still going strong. A fairly decent pair will cost around £40.00 but I reckon you can get fully kitted with jacket, pants and goggles for around £100.00.
I cannot recommend getting your own boots enough, but funds may be an issue. They are THE most important piece of equipment and will last you for years. Some peeps I know bought themselves skis and still hire boots. Absolute madness.
Anyway, enjoy your trip, I am heading out to Serre Chevalier tomorrow to hunt some off-piste powder with my boarding crew.