Registration for scientific conferences of 2/3 days usually cost something between 400 and 600 €.

Registration for ASPO-5 costed 150 €.

Compare.

I can't compare. I'm so poor I can't even understand these numbers. Plus, I've never been to a single one of these conferences. Probably because I can't afford a plane ticket. Please compare for me. I am grateful my sister let's me look at her computer.
Early registration for Hydrovision (1 day longer, less compensation for speakers, 4 sessions concurrent, 2,000+ attendees) was $650.  Large exhibition hall got more $ from commerical companies exhibiting.

Best Hopes,

Alan