If this is done in conjunction with replacing a walkway, there will be little, if any, additional cost. Inside the home, there usually aren't many steps that are easily eliminated. Another approach that works well is to prepare for single-level living. That means making sure the full bath, kitchen and main bedroom are all on one level. Having laundry facilities on the same level is also a big plus.
Maneuverability is most critical in the kitchen and the bathroom.
Use floor surfaces that don't become slippery when wet. Widen spaces and doorways. Whenever possible, design doorways that are 36 inches wide. While you don't give any thought to them when you are fully mobile, they present real obstacles to wheelchairs and other wheeled devices. These changes will not only make your home wheelchair friendly, but also give it a more open, spacious feel.