Been in your shoes before and I understand the dilemma.
RM100 is not much, but it should be enough to get a decent look. Here's my suggestion:
Firstly, forget about your B&D. What it's good at is only for APPLYING products and you'd need to change the 'bonnet' often, or else it would cause more damage than good.
So, I'd suggest you go back to the olde 'elbow grease' if you want to do any decent polishing. Otter Polishine is quit a decent paint cleaner or very mild polish so get yourself a few of those good quality round foam pads (e.g. from Meg's, Osren aka Lake Country pads, etc.) and a few microfiber cloths and polish away with the Otter polish. One thing that you'd need most using this method is PATIENCE. Do it one small section at a time and finish off one panel at a time. This way, if you get too tired (or bored) you can always stop, wax that panel with your Otter Premium Wax and continue with the other panels at another time.
And another product that you should think of getting is a compound to remove those deeper defects (e.g. scratches, deep marring, deeper swirl marks, etc.). My suggestion would be Meguiars Ultimate Compound. It is a little expensive but would still be within your budget.
If you're going the rotary route. Basically you'd need a rotary (of course), a backing plate (the thing that you 'screw' to the machine and to stick the pads on) and AT A VERY LEAST 2 polishing pads. I used to own a china made Ken rotary and got it for RM170 and it was able to give me quite a decent finish. But the poison got deeper and I was getting a bit impatient (also had some extra bonus) so I went for the Makita for the higher amp and torque. I would think that those China made rotary would be good enough if you're not planning to use it often, but, like what kc said, you'd have to bet your luck with it's reliability.
Now for the polishing pad, this would be something that you don't want to cut any corner. Polishing pad would be like the tires to your car, and you'd definitely need to think about getting a good quality ones, and I'm talking about spending around rm60 per pad. And you'd also need to reserve some money to spend on polishes as most polishes that's selling at the supermarket are not that suitable to be used with a rotary.
All in all, if you want to go the rotary route, you'd need an initial budget of around RM400 ~ RM500.
I think you get the rough idea now, and I also think that you have quite a few more question to ask



....so ask away and we'll try to guide you as best as we can.
Regards.