Hot soapy water with just a little de-greaser (easy to do when the piece isn't in the car!) and then the aerospace stuff
To be honest I'm not sure how the sellers make any money. I bought 10 stainless steel self tapping screws which were delivered in a padded envelope by second class post for £1.29. Just the bag and postage would have been most of that!
I know what you're saying about a local hardware store. Those places are perfect if you're fabricating something and need to buy an item to use for something it wasn't intended for - there's no replacement for taking a tape measure to something on a shelf. But for buying things that like this eBay is just so convenient. I can order bits ad hoc on the train to work and it uses up none of my time or fuel. A couple of days they pop through my letterbox.
A future project (i.e. winter tinkering) might be to make use of those blanks on the fuse box cover:
I hate seeing blanking plates in a car. If I end up fitting the heated front screen then that's one taken care of. I'm considering fitting a hidden Bluetooth speaker somewhere in the car so I can stream music (and sat nav instructions) from my phone. If I end up putting that on a switch rather than just the ignition then that could be another one. I'm still thinking...