Delta and Virgin Atlantic have round-trip flights from Houston (IAH) to Glasgow (GLA) for $617 with a connection. Flights in April, September, October, November, December, and January. Departures on Monday, Tuesday, Wednesday, and Sunday. 7-day minimum stay required. Holiday blackouts.
A Carry-on bag and also a personal item is allowed for free on Delta. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.