Ok granted, not a lot of money but
Flying into BWI from Dallas because it costs nearly $165 more to fly to Providence ($110 to arrive early afternoon)
Taking Amtrak (overnight train) from BWI to Providence (total: $65.00 one way)
in Providence for 3 days
Taking Amtrak (overnight train) from Providence to BWI ($65.00 one way)
in Baltimore for 4 days
Flying from BWI to Dallas ($110)
Total cost: 350.00
Flying round trip to Providence = 550.00 (minimum and at shitty flight times taking up the whole day)
Eat that, Priceline!