The honest cost range
Self-drive Kruger (SANParks camps): from ~R1,500–2,500/person/night all-in — camp, park fees, your own food. That's the floor, and it's genuinely good. Eastern Cape private reserves (off-peak): ~R3,500–6,000/person/night all-inclusive. Sabi Sand / Timbavati lodges (peak): R8,000–20,000+/person/night. The range is roughly ten-fold; know which one you're booking.
The biggest lever
Self-drive Kruger. Everything else is a step up. If budget is the constraint, the SANParks self-drive trip isn't a compromise — it's the real safari, just without the butler. You give up off-road driving and night drives; you keep the animals, the dawn, and the silence.
The false economies
Don't book one night at a lodge to "try it" — you lose most of a day to transfer and check-in. Don't pick a cheap lodge three hours from the airport — the transfer cost and the lost game drive eat the saving. Don't go in peak (July/August, Christmas) and expect budget; go in the green season (November–February) when lodges discount and SANParks has availability — you trade easy viewing for price and space.
The one upgrade worth it
If you can stretch, spend the money on a private reserve for two nights after a self-drive Kruger base, not instead of it. The off-road, night-drive, walking-safari experience is genuinely different and worth the splurge once; Kruger gives you the volume.