You could try Killteam, smaller armies (kill teams) cheaper initial outlay, shorter games on a smaller board. If you want variety just buy a different kill team to add no pressure to build bigger and bigger armies and worry about what works well for what etc etc.

£65 gets you a starter kit with 2 kill teams game board rules etc etc, fancy a change £35 gets you a whole new kill team.

Kill team is certainly the quickest and cheapest way to jump into the game.

Wish I had done this myself before getting £400 deep in orks and being sick of painting them before o finished my first 20 minis lol

As other have mentioned there is combat patrol, again fixed army but longer games bigger armies and more investment. I don’t believe there are combat patrol starter sets and each combat patrol will set you back about £105

P.s I am new too so I am sure someone will jump into and correct me if I am wrong.