Approach the whole issue from the opposite direction. But you get the point. If an antagonist needs money to give her sister necessary medical care, then perhaps someone can use her against the party by offering her money. They aren't just for PCs. If there are interesting things going on in town, then there's no reason why the PCs should be the only ones who decide to interfere.
Antagonists can be just as inquisitive and pushy.
They also don't have to get involved at the same point that the PCs do - they might get there first, or come into things much later. They just happen to decide that they want something a little bit different out of the situation than the PCs, and that sets them in conflict with the party. The antagonists might work for someone who has an interest in certain areas. If they're researchers, then give the PCs reason to interfere with their research. Or the company they work for sends them after something that the PCs have, or have influence over.