For an AG, I think it really depends on the install; I had a 18 ft Intex for 5 years, had to replace liner once (about $150)... but it worked great! If you're looking for only 2-3 years, Intex has a 21 or 24 ft now for $7-800, I think...
If you think it may become 7-8 years instead of 1-2, I don't have any advice.