From Bangkok, You can get to Siam Reab by air or by bus. Bus fare range from 200 baht to 600 baht, depend on where you buy your ticket. You may pay 600 baht and the guy next to you on the same bus may pay only 200 baht, so shop around if you decided to go by bus. Prepare to pay up some money at the border. A medical clearance document can be "purchased" at the border, and it was a requirement to cross into Cambodia.
Once you cross into Cambodia, prepare for bad road condition and prepare to pay more on crossing bridges. The locals purposely dig out the bridges or big holes on the road, sometimes the bus cannot cross so you have to change bus, you may or may not have to pay. But to walk across some temporary bridges because the original one was "damage", you will have to pay.
Siam Reab is a decent place. I stayed at the Angkor Wat Guest House. It is clean, private bathroom and only US$3.00 per person.
You can/have to hire a matorcycle taxi to take you around to see the 30 plus temples. I strongly recommend the 3 day pass as it is impossible to soak in the beauty of Angkor in one day! A good motorcycle taxi driver will be a good guide and can take you to even the less known places.