Id check ebay. they have tons of them and sometime are really cheap. good name is viper, or bulldog. there are a lot of manufactures of alarms. check the net see what there is. many alarms have different options like autostart. autolock, tons of features. get what best fits your needs.
For veichile security there is nothing better then the compustar excellent alarm no issues and you can't complain since you also have the paging features as well.
Saved my car once, lol lil punk tried to break in but the alarm paged me and well someone got hurt needles to say it wasn't me.