What route of transportation between Oxford and Amsterdam optimizes economy and convenience?

I am making a trip to Amsterdam in late September for a beer festival for 5 days, and I am trying to determine a means of getting there and back to Oxford that is both easy on my wallet but not overly strenuous or inconvenient. The other restriction causing me trouble is that I will be meeting my friends who are flying from Edinburgh to Amsterdam and will be arriving fairly early in the morning. As such, I also want to try and arrive sometime in the morning on this day (a wednesday if it makes a difference). At the moment, some options I have come up with are:

1. theairline by Oxford Bus Co, period return to LHR (£29) -> return flight from LHR (~£95 at the moment, KLM)
2. book Oxford Tube via megabus.com (£1 fares but somewhat unpredictable in terms of times they are offered for and the length it will take... if the megabus booking isn't possible, one can always just get a student period return on the Oxford Tube for £15) -> London Victoria -> take the tube from Victoria station to LHR (~£5) -> Return flight from LHR (~£95, KLM); this route could be quite a bit cheaper if the megabus deal works out, but obviously more of a hassle
3. theairline period return to LGW (£37) + return flight from LGW (~£90, BA)
4. I have stumbled across a train and ferry option offered by DutchFlyer. Taking the overnight ferry on the way over with a cabin and the day ferry on the way back without a cabin, the fare would total to £120. However, I would need to get to London Liverpool Stn which is where the train ticket included in this fare is valid from. So again, I could attempt to swing some sort of megabus/Oxford tube deal to get to this station. This sounds quite leisurely, but there are a number of changes involved, and I am wondering if anyone can recommend this in terms of convenience.
5. megabus return from London Victoria Bus Station (I can't book far enough in advance, but prices look like they are about £45-50); although this is by far the cheapest even with the bus to and from London Victoria from Oxford, I would need to do the overnight bus with a total travel time of ~10-11hrs. Has anyone ever done this before and is it feasible to get some sleep?

These are only the options I have come up with, so if there are any other suggestions or ideas I could look into, please share.

P.S. I have looked into trains from London to Amsterdam, but the prices seem to be just extortionate.