The type of guitar you'll end up buying depends a lot on what type of music you want to play.
Do you want relaxed, laid-back Sunday afternoon stuff, or do you want the neighbours to think that they're in the back row of a Linkin Park/Megadeth concert?
From my experience, a nylon string acoustic (Spanish guitar) is a really affordable way of learning the basics of guitar playing. Nylon strings are the most gentle on your fingers, and won't hurt nearly as much as steel strings would. If you don't have a lot of cash on hand, consider getting one of these. The price could be anything from about R800, R900 upwards. Just keep in mind that once you have learnt the basics, you're really limited in the sound you can produce. Don't even try playing along to Metallica or Korn or Slipknot (unless you want to go unplugged

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Steel string acoustics have give you an amazing sound, but I found them to be the most difficult to play - especially if you're starting out (this one actually put me off guitaring for a few years, until I decided to give it another go). Generally steel string guitars also feel big and bulky, so I'd strongly advise you to first go to a music shop and try this one out before buying. One of these would set you back anything from about R1200, R1500 upwards.
Electric is the absolute champ when it comes to learning to play. Although electrics also have steel strings, it's nowhere as difficult to play as an acoustic steel string or even a nylon string. The is due to the fact that you have automatic amplification on the sound you produce, which doesn't require you to press the cords down and strum as hard as you would on an acoustic guitar. Simply put, if it’s too soft, turn it up!!
You can also fit a much lighter gauge (thinner) string than you generally would on an acoustic steel string, which makes things easier on the fingers. Keep in mind that the thicker the string, the more difficult it is to play, but the better the sound quality. You should be able to pick up a very basic electric for anything from a R1000 upwards, but this would probably be a no-name brand (Don't expect to be able to sell or trade this in at a music shop either).
You should be able to get a decent, affordable, known brand electric for about R2000 upwards. Have a look at Cort, Squire (owned by Fender), Ibanez, Washburn and maybe even Epiphone (the cheaper version of the Gibson). If you have real bucks to spend, check out Gibson and the American Fenders.
With the guitar, you'll have to get an amp - plan on spending anything up to R1500 for a 10, 15 watt amp. Obviously, if you want more knobs and buttons to give you different effects (channels, chorus, distortion, drive, etc) expect to cough up more.
Also keep in mind that every brand amp sounds different, but if you're after fat, crunchy, distorted sounds, check out Marshall's range (These can be quite pricey though). Also have a look at the Fender amps. There are actually so many different brands of amps, the best would be to browse around music shops, look at the prices and when you have an idea of what you want, ask the sales assistant to try them out for you so that you can get an idea of the sound you can expect.
You can even check the music shops for combo specials, they sometimes do cool deals if you tell them you want a guitar and an amp (they might even throw in a carry bag, strap, guitar cord, a couple of plectrums, etc.) Be sure to mention to them that you want a guitar AND amp!
I would suggest that you visit a few music shops and try out the three different types of guitars. Explain to the sales person that you want to start playing guitar but that you're still deciding which route you want to take (steel- or nylon string or electric).
Even if you can't play two cords in a row, sit down with the different guitars, get the feel of them, feel your fingers on the fret board, etc. Maybe even ask the sales assistant to play something so that you can hear what the guitars sound like.
As far as lessons go, unless you know someone that can teach you the basics, you should really consider going for lessons. This can also be expensive, R100, R200 per (hour) lesson, R300, R400 per month (4 lessons), whatever. Chat to the guys at your local music shops to find out about this, usually guitar tutors leave their details at music shops.
If you are located in the JHB area, I could point you to a couple of good music shops.
Last bit of advise, shop around! Don't buy the first best affordable guitar you see. What you buy now is either going to put you off guitars for a very long time, or it's going to make you fall in love with it forever
Have fun and keep us posted.