There are not many organizations advertising volunteer work in Senegal currently, the following three organizations hopefully provide an excellent starting point for your search.
Below I have listed two organizations offering cheap volunteer opportunities in Kenya. If neither of these organizations are what your want, I recommend you look for volunteer opportunities while you are in Kenya. There are dozens of small organizations that would love your help.
Amurtel - Charity based
in India that runs children's homes in Kenya. Women volunteers work 2, 3
or 6 months. Simple vegetarian food and accommodations provided; volunteers
contribute $250 for short stays of 2-3 months and $400 for longer stays.
Friends of Tsavo - Arose as
a result of a growing need to protect and conserve the natural diversity of
one of Kenya’s most important national parks, Tsavo National Park.
Tsavo Conservation
Trust - Volunteers participate in a variety of volunteer opportunities
in rural Kenya and contribute $177 per week to cover costs. Basic computing
training also required; shared accommodations available for $7.50 per night.