Hi, what's better for an acme screw, stainless steel or zinc plated?

I'm new to this group... someone was kind enough to point me to this
group.

What's better? Stainless steel, or zinc plated acme screws?

The specs for them are 1" dia, 5TPI/Pitch...
Stainless steel is expensive...
$30CDN for 3'
or
$75CDN for 12'

Zinc Plated is CHEAP...
$11CDN for 3'.

Plus the appropriate bolts (which I don't know what to get yet)

--
Lloyd Leung