I just spent the weekend building a wheelchair ramp for my 85 year old mother, and thought I'd pass this along to anyone who might be in the same space with a loved one or neighbor who could use a ramp.
There is a wonderful web site out of Minnesota -
2x6, support posts 4x4 and rails of 2x4s, all pressure treated, bolted and nailed or screwed. Two of us worked 8 hours this past saturday, and I put in another 7 sunday, and got the base framing and supports in for a 40 foot ramp (1:12 slope) with only the decking and railing to finish up tomorrow, so I'd figure 3 full days (I did not pre-construct sections as they suggested.) Your cost will vary depending on the vertical drop you have to achieve, but for a 33 inch drop at a slope less steep than 1:12, I came in at around $1500 of material.
Mutt