Infinity has a small buy in for models. The newer minis are less "awkward" than earlier minis that sometimes felt like to were having to glue on each finger on a model. There is a boardgames coming this fall.I know there's Infinity, but I'll be honest - full lead Infinity scares me. It really looks intimidating.
I'm really not sure if I want to throw in with Kill Team. I had one player tell me its based off of last edition's 40K rules, is fiddly, and isn't really good for casual games like I want.
What else is there in sci-fi?
Kill Team is based on the current edition of 40K. It have everything you need (save models and terrain) in a single 208 page book. That's rules to play, scenarios, army lists for most 40K armies, specialist rules and is about as complex as basic D&D without spells. This probably is the game you want. The only reservation I have is that it has had 2.5 expansions and I feel like they might revise it soonish like they did...
Necromunda is GW's other skirmish game. While set in 40K, it is not like 40K and has its own rather rich and distinct setting. It is also based on the current edition on 40K, but adds lots of details--for each character. In Necro each character basically is it's own D&D character with unique (from other characters) skills and equipment. It's meant to be played long term as a campaign so your gang evolves over time. People can get very attached to their models as they start to see them as characters rather than replacable fodder. Necromunda was released in 2017, but has had all its rules combined and refined into two books (rules and gangs). A third book has no been released, which is getting good reviews even by people sceptical on the new game.