A lot of kids go through this time where they have been separated from things that represent their interest(s) and their childhood. You are not alone. Finding affordable Legos can be hard but not impossible. If you are lucky enough to live near a Lego store you can buy pieces from the wall as a cheaper alternative. Sometimes you can find decently priced sets online at resale sites. They are almost always missing some pieces. You can save money to buy a set that hasn't been released yet. That gives you time to save and the opportunity to find a new set you really want.
There are many, many adult Lego enthusiasts. You can look forward to having this hobby for years to come even if you cannot participate right now.
In the meantime you can enjoy Lego's Digital Designer.