Hi! I've been doing shade and native-plant gardening on a shoestring for about a decade outside Washington DCA. A few ideas:
Along with your Amelanchier/sarvisberry, think about getting a dwarf pie-cherry tree. Northstar is a good variety, and you should get enough fruit for a pie after about 3 years, if you start with a three-foot tree. You only need one to get fruit. I got mine for about $20.00 at that height. Another lovely is blueberries, though it takes two of them to get fruit -- ideally of different varieties. The blossoms are white and fragrant, and the leaves turn nice colors in the fall, too.
If you're already building a compost heap, your neighbor's grass cuttings could be a good addition, provided he doesn't use all sorts of chemicals. I layer chopped brush, grass clippings, kitchen trash, stable sweepings and a bit of lime, and I get great black soil in about four months in full sun, six months in shade.
My county has leaf mulch and bark mulch for free at central distribution sites; I mulch my beds with about 3" of the leaf stuff each spring (bark looks better, but is not broken down as readily, so it ties up nitrogen). It keeps the weeds down; the worms incorporate it into the clay soil by midsummer (at which point I put on another layer if there's still any left) and after five years of this you can really tell the difference. Have you heard of "Lasagna beds"? You can make new (semi-raised) beds by heaping up the same layers as for compost in the fall, about two foot thick in toto, and it rots down and combines over the winter so you can plant into it come Spring. I believe there are websites descibing the process. And all this is free!
A good book to look for is "The 20 Minute Gardener". I'll look through my library for good Native Plants books tonight.
Lynn Title Washington DC area, zone 6-7