Returning to 40K - How to restart Astra Militarum

Hi everyone, I used to collect Warhammer 40k with my dad maybe 15 or so years ago. I've kept my interest in the setting and played games like Spacemarine 1 and 2 over the years. I am wanting to get back into collecting and maybe even playing warhammer. However I am busy with work and life so I don't want to spend loads of money and then not get back into the hobby. How should I go about buying my first new kit, paints, etc. without breaking the bank? I am happy to buy even just a small unit to dip my toes back in the water! Thanks in advance.

TLDR: Looking to get started with astra militarum without spending too much as a retuner to the hobby.