You'll find plenty of taxis in Aswan, the same six-seater Peugeot station wagons as in Luxor. You can travel the length of the Corniche for about £E20; shorter trips cost about £E10.
You can also use taxis to travel outside Aswan; just remember that police permission must be requested at least 24 hours in advance. Approximate costs for Peugeot taxi service from Aswan—as quoted by the Tourist Information Office—and covering up to four passengers in the same vehicle are as follows: £E120–£E150 round-trip for the half-day, 90-km (56-mile) journey to Kom Ombo; £E300–£E350 one way for the full-day, 225-km (140-mile) trip to Luxor, including stops at the temples at Edfu and Kom Ombo. You should expect to pay about £E70 round-trip to Philae, including the driver's two-hour wait while you visit the temple (you'll also have to hire your own boatman if you go independently). But it may cost the same, about £E70, to add the High Dam and Unfinished Obelisk to the Philae route.