Marketplace
Pay What You Want ($1+ US for Steam Keys)
Steam Marines — Normally $14.99 US
ROCKETSROCKETSROCKETS — Normally $6.99 US
StarMade (Early Access) — Normally $9.99 US
Pay More Than Avg (currently $4.04 US)
Interplanetary — Normally $14.99 US
STARWHAL — Normally $11.99 US
Edge of Space (Early Access) — Normally $12.99 US
Pay More Than $10 US
Reassembly — Normally $14.99 US
I already had most of these games on Steam, but bought the $10 tier as Reassembly looks really cool and comes with a DRM free copy as well (which is always good in my opinion). Starwhal and RocketsRocketsRockets should be some multi-player couch co-op fun.