The family became wealthy again in late 2008 / early 2009. Cheryl's breast cancer storyline didn't begin until 2012. (I know LWA continuity doesn't completely line up with regular Archieverse continuity.) There's no indication in LWA that they're poor. In fact, when Cheryl returns home, she's living in a mansion. It's simply unspoken regarding how her initial treatment was paid for and who knew what when. All that's certain is Jason didn't know anything until after she'd had the mastectomy and lost her hair, by which point she was gaunt.