Depends on what your trying to shoot. Your On-Camera flash is only good for close areas & they wont give you the coverage of using a external flash that is purpose built for a larger area. The on camera flash can't be used with a loom lens/lens with a hood either as its not high enough to clear the lens therefore casting a shadow in all your images. Plus On Camera flashes are very harsh & images look like crap.
Canon makes the 430 or the 580 if you are into serious stuff. Here they cost about 50k & 65k. If you can get it down it would be way cheaper. There are other brands like Nissin, etc which are about half the price but don't really cut it.
Try not to use the flash, & make use of the ambient light, the shots look more natural . If your lens is not that fast, there are cheap lenses that can get you started like Canon's 50mm f1.8 II probably cost about 10-15k here. And you then learn to make use of more of your camera's features. There are loads of links on You Tube that will give you a better idea as well