You don't necessarily need an expensive or specialized camera to take photographs of butterflies. Many of today's compact digital cameras are capable of capturing remarkably good closeup images. That said, I've been using an SLR with a macro lens pretty much from the start.
As far as brands go, I shoot Pentax.
Back when I was shooting film, I was using an old 70's era 100mm macro lens on a couple of different SLR bodies ( chiefly the MX ). It was strictly manual focus and manual exposure control. For smaller butterflies, I'd sometimes add an extension tube for extra magnification. A few of the images on this website are scans of shots from this period.
In 2009, I finally decided to switch to digital and Pentax offered a relatively inexpensive upgrade path. I could continue to use my old Pentax-M 100mm F4 macro lens on a new digital camera body. I selected the Pentax K200D, a mid-range DSLR, as it offered weather sealing and in-body image stabilization. So with a modest investment in this camera body, I obtained a rugged, image stabilized macro setup. Many of the images on this website were captured with this lens/body combination.
Early in the 2012 season, I replaced my old macro lens with a new Pentax DFA 100mm f2.8 WR macro lens. The new lens is a definite improvement, but the old glass was not so bad. There are a few images on this website captured using longer lenses, which I resort to when I can't get close to my subject, but the 100mm macros ( old and new ) have been my primary workhorses. A few years ago, I upgraded my body to a K-30, but I'm still using the WR macro lens.
Though I did experiment with flash photography early on, I found I preferred the results obtained with natural lighting. Having a flash attached to the top of your camera can be awkward when you're hiking through dense undergrowth, and I personally find that I don't like to have my gear placing restrictions on my mobility. Other photographers use large and complicated rigs. Different strokes...
The images featured on this site were captured using only ambient light without the benefit of a monopod or tripod.
Bottom line: I'm not using super expensive equipment. My advice is to learn to make the best use of what you've got before investing large sums of money in fancy gear.