There are many levels of gardening and landscaping that can be done.. a couple different budgeted ways to garden are:
For free you can clean up existing plant beds. Remove the weeds, dead plants and overgrown plants. Prune the shrubs, just remember not everyone likes square bushes! Trim tree branches that hang to low and discard any that can create a danger.
For around $100 you can create a welcoming entrance with one or two big pots filled with colorful plants and flowers. A few 5-gallon trees for about $30 each can make a significant impact on the landscape. Buy seeds (maybe a mix of wildflowers) that cover much more ground than $100 worth of plants.
For around $500 you can great pots that make a statement for the entrance. Add seasonal planting of ornamental grasses and colorful annuals in or around the pots. Benches or garden ornaments (birdbath) can make a yard look wonderful. Plant long blooming perennials around the boarder of the house. Add light fixtures to highlight plants and walkways. You can always add a nice door wreath to complement the change in seasons.