How much do you think it would cost, to install a power steering unit
In a 2003 Toyota echo.

Pump ($300+labor) and rack & pinion ($405+labor).

In the future, since most Toyotas I've seen use Dexron ATF in the power steering system, use Mobil 1 Synthetic Multi-Vehicle ATF. Then, you should never have a problem again. I recommend using a battery squeeze bulb and partially changing the fluid, with Mobil 1 ATF, every 40,000 miles.