Installing a strut bar is incredibly easy. Just make sure you tighten the strut mount bolts back to the specified torque with a torque wrench.
TRD makes a very nice strut brace, but they are very expensive.
You can get a universal one for cheap, but they aren't as stiff because they are adjustable and might be made of heavier material that is not as stiff, like steel versus titanium.
The TRD brace for 03+ is $125 at any number of online places.
Prices go down from there.
Do a Google search for "Corolla Strut brace"