My city offers low interest loans to elderly people to fix up their yards and homes.

In some areas there are grants and/or plants available to individuals who wish to create Rain Gardens.

You might want to check in your area.

Hmmm.. Well, nothing that I know of. I know it can get expensive….

Look in the local paper or on one of the following sites:
People will somtimes give away supplies they no longer need/want, or atleast will sell very cheap.

And, for some frugal gardening tips:

(might give some ideas?)