I'm looking for a neon lamp that actually produces a good amount of light, like the ones used for runway lighting, or a small straight one.

Does anyone within the EU have one for sale?

I have so far asked one neon lighting shop, but a very basic tube would already cost several hundred euro which is too much for me.

Ask another neon shop, a small straight tube is a 30 minutes job for them including processing, it absolutely should not cost hundreds of euros. May be in some neighboring country like France or Germany.

https://www.neon73.nl I believe is still in business.

Yeah, that amount sounded very high to me. I was kinda struck down a bit after hearing the price range being >500 euro.

I will send that company an e-mail.

If anyone knows other companies that are worth asking, do let me know!

This isn't exactly helpful, but I know pedestrian signals over here, as well as the USA, were lit with neon tubes.
https://www.hobbiesplus.com.au/signspotters/traffic_signals.htm