I've had the same basic D-Link ADSL Modem for about 4 years - the 2500u.
You can get them for around R200 or less. Been extremely stable up to now; subsequently attached a TP-Link TL-WR841ND Wireless router to it, and both work well together.
The D-Link 2750u is a wireless modem/router in one, approx R600, last time I priced them - have read conflicting views on them in this / other forums, so it's a case of take your pick, and hope for the best !