Perissa is a good an a very nice place to stay and yes some of the cheapest hotels are there It will depend what time of the year you are planning to be there as well. Another option will be Imerovigli Thats the highest point that overlooks the caldera, more expensive than Perissa but hey how many times in your life you can sit and enjoy the sunset on at the biggest balcony of the world
This place i have stayed and know well uranoshouses.com There are many others as well all with the same view You can find then at santorini-hotels.info/santorini-island-map-hotels/hotels-in-Imerovigli.asp and greekas own site
http://www.greeka.com/cyclades/santorin ... /index.htm
Best of luck
