cheap flights?

Checking when you are flying via things like kayak.com or skyscanner.net is the best way to answer your question. It may be cheaper to fly into London and then to Dublin with someone like Ryanair (leaving plenty of time between the flights - I'm looking at August flights to Washington and it is cheaper to go from LHR than it is Dublin by about GBP100). I suspect the question will depend on all sorts of commercial factors and luck rather than a guaranteed rule. You shouldn't hitchike or if you do then you need to realise the risk and that it may not be easy (although if you have hitchiked before you know that).

Some of the Boston flights stop at Shannon, but check out Aer Arann

Its really cheap sometimes to fly direct from the States to Dublin or Shannon, just keep on eye out on airlines websites.

Direct flights from America to ireland

Delta fly direct from Atlanta and JFK

Aer Lingus fly direct from JFK, Boston, Chicago, LAX, San Fransico, Washington.

Continental from New Wark,

US Airways from Philly

Also some Air Lines which fly to India and Middle East from the States stop in Shannon to refuel, so you can get a deal with them as well, dont bother flying to London, just going to give an extra immigration line to wait in and hassle

If you are flying in late summer the USA Customs Pre-Clearance in Shannon will have opened. This means that you will be able to make a connection in the states and check your bags right through to your final destination without having to pick them up and re-check them.
Up to now it has been such hassle making connections in the states from international flights that a lot of people paid the extra for the direct non-stop option.

Travelling from Boston this year, we have found the best value to be on Delta via JFK to Dublin or Shannon. It changes all the time but that has consistenly been cheaper, often cheaper than getting on the flight from JFK (airline logic)
Another one that has come in cheap lately is Delta (again) BOS-JFK-CDG-SNN with AirFrance operating the CDG-SNN leg (if you don't mind doing the extra leg into France. )

#3, OP said no worries about discomforts or delays; I was almost going to send them to Kiev and back via WizzAir to Luton and then Ryanair to Dublin.

Check out article in Irish Examiner today http://www.examiner.ie/ireland/aer-lingus-to-offer-euro80-fares-to-lure-us-tourists-94221.html