3 packs of washers and a pack of bolts came to £6.67 (1 up on satan, hehe).
I didn't bother with the nylon washers on the last one I did for someone, it worked fine, people only recommend them to save them from making any contact but there's nothing around that area on the motherboard that can make any contact as far as I could see.
Also you only need 1 washer on the underside of the motherboard too, I've no idea why people are suggesting to put 2 on the underside.
I guess if you can find nylon ones then go for it but it's definitely not necessary.
I would be interested to hear what people have been using to remove the old thermal paste though.
As far as arctic silver is concerned I always buy mine from either scan.co.uk, dabs.com or aria.co.uk. I worked for PC world once, I refuse the fund their bullshit behaviour any longer
Keep rockin dudes