This is probably a stupid question. Is this ability spending 1 point to be able to cast summon monster from a normal spell slot or as an SLA?
You spend a point to cast it as an SLA. Something like that would normally tell you if it consumed a spell slot and the ability is designated as (Sp).
Note that as raw, the higher level you are, the more expensive it is regardless if you want to use it at lower level as it replaces its function as you level. Of course, every DM that I've asked about this has let me use it at its lower levels for its cost per that level, but I just wanted to warn you.