flights to Guatemala / Honduras

Try COPA from Santa Cruz to Panama City and then transfer. COPA flies to many cities in Central America.

You will always find the cheapest flights from Lima.

I second the recommendation on Copa, a Panamanian airline.

Avianca, a Colombian airline, is also one you should look at.

If you're far from Lima, you can get there cheap via bus if you some time and some guts. I did a 40 hour haul this past week from central Bolivia to Lima. It cost me 100 Bs and 80 soles. I did it for about 45 bucks, but probably could have done it for 30 also...

Flights from South America to Central America aren't cheap so don't expect a bargain.

Out of Santa Cruz de la Sierra, take a look at Copa changing planes in Panama. Out of La Paz, take a look at Avianca changin planes in Bogotá (to Guatemala) and with two changes of planes to Honduras (either San Pedro Sula or Tegucigalpa).

Out of Lima, take a look at Copa (changing planes in Panama) and Avianca (changing planes in San Salvador).

Out of Lima, you could also look for a one-way flight to Fort Lauderdale (with Spirit or Jetblue) and another one way from Fort Lauderdale to Guatemala or San Pedro Sula with Spirit. Verify the schedules to see if they match; i.e.: if you can make it in a single day, if you would need to stay overnight in Fort Lauderdale, if you would need to wait several days in Fort Lauderdale... and don't forget to verify the requirements for people of your nationality to entry or transit in the USA.