If you do opt for the trangia bottle, go to www.mapandcompass.co.uk as they do quite a good deal on postage.
I have recently found some industrial meths (clear, not dyed), and at the moment, I'm using Listerine total care mouthwash (pale purple), so my meths looks like water, and my mouthwash looks like meths !I have a thing about the right tool for the job so I would prefer to use a purpose designed bottle to carry around my highly flammable smelly meths but if money is tight and you are going to use a plastic bottle then maybe an empty mouthwash bottle would suit the job. They have a safety cap so they should not open in your pack. I would still use the gaffer tape to identify the bottle though.