You should consult a lawyer, but typically a patent can be enforced if all the claims are met.
If your new startup does something similar, but with enough variations that you can prove doesn't meet all the claims (here is where you need the lawyer), then you're good.
Patents of different classes of claims, dependent and independent, for example. Some stand on their own, some don't. Patents encapsulate lots of claims, and violating any one of them can represent a significant IP infringement and could lead to damages.
Your advice about 'enough variations that you can prove doesn't meet...' is dangerous. What you mean to say is that, "if you are willing to spend up to and potentially beyond $100,000, a jury might make the determination that you did not infringe." Lawyers don't determine whether or not you infringe, juries do. And, the most common resolution in IP is ceasing activities or licensing, which are usually settled out of court.
If your new startup does something similar, but with enough variations that you can prove doesn't meet all the claims (here is where you need the lawyer), then you're good.