You still need to connect and two airlines almost always cost much more than one. Iberia started using GUA as a connection vs. MIA to Spain, so maybe you can do Iberia to GUA and TACA to Teguc.
The main problem is from SDQ there are not that many destinations - Cuba, Panama, Caracas and the USA , apart from Europe which is not really a suitable connection point.
Actually consulting my GDS there are 2 choices AA arriving around noon and Copa at 1That's it. Copa's V fare if available is cheaper by about $50.