I do not live in your area, however I do not believe your question should go unanswered. You can contact a local Realtor and have them send you some listings so you can compare rental prices. Also you can check http://www.Rent.com, http://www.Craigslist.com and the classified section of your local newspaper, this will give you the best info on Rental costs in Manayunk.
Best of Luck,
Century 21 Infinity
I know you posted this question a while ago, but are you still interested in the Manayunk area? I live in Roxborough, which is right next door to MYK.
Let me know if I can be of any assistance.