You bet I can tell you about McAllen, Texas. I have lived here for 14 yrs. It's hot and humid 3/4 of the year. The remaining 1/4 is our winter which is really like spring. Your right the cost of living compared to San Diego is low.
If your a outdoors person like me, take my advice and look in the area of Bayview, Texas for buying some land and building a house. Here is a website that will give you some ideal of what the Rio Grande Valley looks like in certain areas. http://raingardens.com/psst/meetings/PSST_Dec03.html
A lot of people travel here in the winter to go bird-watching in the the Rio Grande Valley area. We have lots of beautiful, migrating birds here. We bought some land in Bayview next to the resaca. I hope this helps you.