gerardo,
If you want some help to find someone to buy a cavaquinho please contact me, I live in Brazil and cavaquinhos are very easy to find around here. They are smaller than the tenor ukulele, they are more alike the concert. There are some smaller models also, called "cavaquinho paulistinha". They are a little bigger than the soprano uke.
3 years ago when I started playing the ukulele, people who was interested in playing the instrument used to strung the cavaquinho with nylon guitar strings, because you couldn't find ukuleles in stores. Importing to Brazil is very expensive. The tax is 60% over the price of the product + shipping, so ukuleles were always very scarce around here. Today you can find Kala and Lanikai ukes in some stores.
Maiki,
I'm a guitar player and at the first time I played a cavaquinho I tuned the first string to E. It sounded very strange, because the usual chord shapes and voicings are very important to keep the cavaquinho unique characters. I find playing the cavaquinho harder than the uke, very unconfortable to play if you are not used to, since the strings are steel and the tension is very high. Also, the samba playing on the cavaquinho requires a great right hand ability and the
Don't know if you knew it, there is a banjo version of the cavaquinho.