Advice on Uganda

Uganda is a cheaper destination than many other countries in Africa. If you just wanna go around with public transport, eating normal food, it can be very cheap. I paid between 10000 UGX to 60000 UGX for rooms, the most expensive being in a national park. The cheapest was pretty bad, but I stayed in a nice place in Kasese for 20000 UGX a night. Double that in Kampala. What is surprisingly expensive (compared to costs of transport, food, simple hotels) are the national park fees. Of course if you wanna have a private car it's also pricey. I arrived in some villages late, they all seemed to have a simple, cheap lodge to stay in.
Your other questions I can't really answer, but I'm sure you can put up your tent, just not in the centre of Kampala.

get the Bradt guide for Uganda very useful. As for accomodation in addition to what Bradt calls shoestring there are often quite reasonable places between 6000 and 10,000 that can be found (there are also some at that price that are best avoided so look first)

you can find my update report to the guide on the Brand Uganda guide update pages on their web

Local food and beer very cheap
no idea about camping (not my scene) nor the volunteering you are looking for

Hope you don't mind if I piggyback on your thread with more questions....

How easy is it to visit the national parks on your own? Are guides really the way to go and what kind of prices can we expect? I'm interested in seeing wildlife other than gorillas.