DISCLAIMER-I do not pretend to know all the ins and outs of Tanzania and I have limited knowledge to certain areas.-
*Where I went and for how long
Tanzania: Iringa, Ruaha National Park, Dar es Salaam (briefly) and Zanzibar, for 3 weeks in total
*What was great?
Being immersed in African culture. I went on safari in Ruaha and saw so many animals up close that for a second I thought I was going to die at the tusks of a stampeding elephant despite it being perfectly safe! It's exceptionally cheap there as well so on the one night I went to a club with my fellow volunteers it would have been easy to get a little drunk had it not been for the limited stock. Whilst on Zanzibar, I went snorkelling and saw so many colourful fish and sea life although there was poor visibility that day. The sun on Zanzibar was amazing, the perfect summer destination. It is such a beautiful country with so much to offer. The local people are exceptionally friendly and the children love playing with "mzungus" (white people in Swahili).
*What was a letdown?
The weather in Iringa. It's freezing at night and the wind howls horribly. Also it doesn't get warm in the day until around 11am so you get a limited amount of tanning time! Similarly in areas such as Iringa it has quite a conservative culture so no vest tops or shorts. Also the long journey down to Iringa is absolutely horrible: around 8 hours on a coach with two toilet stops: one in the middle of nowhere with long grasses to hide yourself and another which I didn't dare leave the coach for. My coach on the way back to Dar es Salaam also broke down for a very long time and since I was only with a fellow volunteer we could not understand what had happened or what we should do! Luckily someone spoke English and told us what had happened. It's very easy to spot tourists there and so you will be completely overcharged for things such as taxis and souvenirs.
*What does it cost to do it bare bones/live comfortably/live like a king?
A minimum of £550 for flights (which includes stopovers), over £1000 for British Airways (direct flight).
If you want to stay in basic accommodation you wouldn't be looking at much more than £10-15 a night but nicer places can be considerably more particularly on Zanzibar which is known for being a honeymoon island. However in Kendwa where my friend and I stayed we managed two nights for $50.
Food is so cheap on the streets but not as much in the hotels. However in my mind this could be that by the time I stayed in a hotel after 3 weeks in the deep south of Tanzania, where effectively no tourists go, everything seemed expensive! I'd say a main meal in a decent hotel is around £4-5 so actually not that much but with the street food vendors you could be looking more at 30p per meal!
Safaris can cost a lot more though. You'll be looking more at £100 for tours and accommodation.
*Tips on being prepared
Medically: Take the best first aid kit possible with proper DEET 50% mosquito spray; they are nasty little things! Look up all the vaccinations you will require as there are a few (for trips to Zanzibar Yellow Fever is NOT necessary - new rule).
Also take most of your cash in US dollars as hotels and safari companies prefer dollars. You can easily exchange money in Tanzania though. Do take some warm clothing as it might not be as hot as you would think.
Internet and electricity is sparse and not entirely reliable in certain parts of Tanzania.
Just be friendly and you'll go far.