Travelling from Lisbon to Albufeira you want to get of at the Albufeira Bus Station. (NOT Vale Paraiso if travelling with RENEX)
There are not always taxis available but my colleague in Albufeira,(Cubsur)(www.algarvebus.info), says
"In fact often as not there are none waiting at all. If there isn't one, call 289 583 230 and they will send one. I am not sure about 4am for example as I have never had reason to call a cab at 4am."