American and United are competing with Spirit Airlines low fares on limited dates in June, July and August with fares as low as $36 to $44 one way in June and $74 to $84 one way in July. Low fare dates are sporadic, so making a round trip with one airline getting low fares on outbound and return can be tough. Easier if you mix and match airlines. I find round trips easier to construct searching one way fares on Google Flights. There are a couple of potential mileage run dates for $99 round trip, but this fare is better for someone who wants a week in either Dallas or Boston and is flexible for June or July travel. I find round trips easier to construct searching one way fares on Google Flights.
American Airlines Boston BOS – Dallas DFW
$108.20 round trip Wed June 8 – Tuesday June 14
American Airlines Dallas DFW – Boston
$166.20 round trip Tuesday July 12 – Thursday July 21
United also has some low round trip fares for travel in August.
United Airlines Dallas DFW – Boston BOS
$163.20 Monday August 8 – Monday August 15