I've started my search and getting confused. Is it extract powder i want? Andrographolides?

Depends on the extract.  If standardized for andrographolides then no.  The problem with standardized extracts is that what the herb is standardized for is generally not the only active compound in the herb.  Most herbs have multiple active compounds that work synergistically.  Standardizing the herb alters this synergy. 

Concentrates are OK, such as the 5:1.  It just means you will take a smaller amount.  So either the straight powder or a concentrated extract would be my choices.

Do some have more of these in than others.

Levels will vary from batch to batch since the growing conditions of the plant can alter chemical levels.

I've seen 5:1. What is the best?

Again powder or concentrated extract.

What should i be paying for say a kg?

For the powder it would be somewhere around $32 a kilo.  I have not priced the extract.  But generally these are cheaper than the herb.  So I would expect it to run retail around $25-28/kg.

I'd buy it from my normal supplier but they don't do it.