There are four different tech levels at every starbase.
These four tech levels are, starship hull, starship engines, starship beam weapons and starship torpedos. You must spend megacredits for each leap in tech level you take. The cost of each jump in tech levels increases as you move up in tech levels.
Your choice of starship components increases as you increase your tech level. The cost of high-tech starship components is far more than the basic low tech version of the same components.
Every starbase's tech levels are independent of all other starbases. When you build a new starbase all four tech levels normally start at level 1. Four of the native races give a tech level 10 bonus for building a starbase.