Welcome back! We have a lot of resources for this on the forum, including these two articles which are a bit old but still relevant:
www.elitefourum.com/t/how-to-have-a-satisfying-collection-by-cbd1235/10807/1
www.elitefourum.com/t/back-into-pokemon-a-guide-for-returning-collectors/13079/1
With reference to your specific situation, it’s totally possible to build an exciting and fulfilling collection without a lot of money. How you spend your money is much more important than how much. The advice for any new collector is going to be to do a lot of research, look through eBay/TCGPlayer/TrollandToad and find some cards that you really like.
It may take some time (and money) to figure out exactly what you want to collect and what interests you the most. But that’s normal! Once you do figure out what you like, stick to it, set achievable goals, and be clear with yourself on how much you’re willing to spend.