(2-part post):
�Hola Brenda, del Reino Unido!
The Answerbank is a UK-based site so we don't have a lot of experts on US domestic travel around here. However, here's what I've come up with:
Your problem seems to centre around the fact that your nearest airports (Las Vegas Municipal and Santa Fe) don't handle the large aircraft which offer cheap flights. It looks as if you'll have to fly from Albuquerque.
Delta can fly you to Jacksonville, from Albuquerque via Atlanta, for $188.50 per adult (including taxes & charges), with departures at 0630 or 0800.
American Airlines' price is slightly higher but the times might be more convenient for you. They have flights, via Dallas, at 1045, 1435 or 1720, for $262.50 per adult (inc. t&c).
United have a flight, via Washington, at 0811 for $238.50 per adult.