It turns out that this is driven from the template's Price PHP file app/code/design/frontend/MYTHEME/template/catalog/product/price.phtml which reads the label values from the locale files and displays it.
So the simple solution is to change the label values in app/locale/en_US/Mage_catalog.cvs:
"Special Price:","Special Price:"to
"Special Price:","Our Special Price:"
"Regular Price:","Regular Price:"to
"Regular Price:","Suggested Retail Price:"
However, the recommended upgrade-proof method would be to create a new locale specific translation file containing only the above desired changes and save it as: app/design/frontend/MYTHEME/locale/en_US/translate.csv.
And don't forget to clear the cache after doing any of the above changes or they may not be visible on the front-end!
Similarly you can change any labels that you desire. Note that this is case-sensitive and needs to be done very carefully.