Sardis is easily reached from Izmir, Manisa, or most nearby cities by bus. To reach the city from Izmir or Manisa, find a company selling tickets to Salihli and request to be let off at Sart (though the company will also understand if you ask for "Sardis" or "Sardes"). You will be dropped off at what appears to be a gas station. Follow the road immediately past the gas station/bus stop, which branches to the right. This road will take you past the gymnasium complex, and ultimately to the Temple of Artemis.
There are two daily trains between Alsancak station in Izmir and Uşak, which stop at Sart town. The Sart train station appears to be about a kilometer from the gymnasium (marked as "Sardes" on Google Maps), and slightly further from the Temple of Artemis. There are also daily commuter trains between Alaşehir and Manisa, leaving Alaşehir for Manisa early in the morning, and returning from Manisa to Alaşehir in the afternoon (making them impractical unless you plan to stay overnight in Sart, Salihli, or Alaşehir).  [formerly dead link]
There are two main attractions in Sardis, and it costs five lira for a ticket to see both. The Temple of Artemis is a ruined Greco-Roman temple, which also has the original crane from the early 20th century excavations. The gymnasium complex includes the ruins of a Roman era synagogue.
Additionally, there are several other sites, shown on maps at the gymnasium and temple, all of which are free to enter, and several of which are hard to find.
Public toilets are available if one walks west from where the bus drops you off, and unlike most public toilets in Turkey, they're free.
Neither of the main attractions has a museum shop.
While there are several restaurants, convenience stores, and tea houses (which serve only simit), all of these are somewhat run-down. The best variety can be found by going into the center of Salihli, where there are several restaurants and a large agricultural market.
Tea can be had at a reasonable price at a handful of tea shops along the main highway to Salihli.