For under 100, you are going to struggle unless you buy second-hand. Even then, I suspect that your options are going to be severely restricted. The Nikon 18-70 should be availabe used for under 100 (GBP) although you may have to shop round a fair bit for it, but even so, just cropping shops form your 18-50 would probably give you almost-as-good results. Maybe Nikon's 18-135 wold be better, but finding a used one, even for your budget, could prove very difficult.