That is about your each way price.

Yes they do. But prices in mid-to-late December will be double what they are in, say, mid-January. Supply and demand, innit.

This is a useful site to search all sorts of flying options :
Matrix - ITA Software

Unfortunately nothing in there that matches your price

Landing in London England on Christmas Day a false economy. There is no public transportation and unless someone meets you at the airport it costs lots for private car hire - "what you save on the roundabout, you lose on the swing".

So when you find this flight to say france or holland for $650 I take it your going to pay for a bus,train or flight to the uk which will probably cost you a minimum of £100 probably more why don't you add that extra £100+ to your flight budget and make it a more realistic $8-900 flight to uk?

agree fully

and I guess the OP missed this one?

update ...for the dates the OP is looking for

$501.06 air transportation charges + $326.86 taxes, fees & charges = $827.92 CAD total price per Adult

Departing Flight Information - Monday, December 01, 2014Flight Duration: 12h 00m

Air France
Flight 351 Departs: Mon Dec 01 6:25pm
Toronto, ON - Pearson International (YYZ) Arrives: Tue Dec 02 8:05am
Paris - Ch. De Gaulle (CDG) Transfers are required between arriving and departing airports Air France
Flight 3164 Departs: Tue Dec 02 11:05am
Paris - Orly (ORY) Arrives: Tue Dec 02 11:25am
London - London City Airport (LCY) Operated by: CITY JET

Returning Flight Information - Tuesday, December 30, 2014Flight Duration: 23h 24mDelta Air Lines
Flight 31 Departs: Tue Dec 30 3:15pm
London - Heathrow (LHR) Arrives: Tue Dec 30 8:09pm
Atlanta, GA - Hartsfield-jackson Atlanta International (ATL) Delta Air Lines
Flight 5031 Departs: Wed Dec 31 7:30am
Atlanta, GA - Hartsfield-jackson Atlanta International (ATL) Arrives: Wed Dec 31 9:39am
Toronto, ON - Pearson International (YYZ) Operated by: EXPRESSJET doing business as DELTA CONN

I don't think the OP has thought this through tbh, if his/her budget was the maximum then they have probably no chance getting to the uk on those dates on a return ticket but then say a flight to France/holland would be ok as they would get home from there?? (didn't know transport was free in Europe) but as you showed with the flights you found if he put together the $650 budget plus his costs from France/holland to the uk then he would get the return flight to the uk easy enough...time to be realistic with their budget me thinks : )

Maybe the OP is happy to hitch or travel by bus which could be as little as $50 return between Amsterdam and London.

Maybe they would and if they do are they going to hitch it back too?...was only trying to be realistic as they would have flights to be on time for if hitch hiking and I don't know of any bus for £25 quid return to Paris or holland, was only trying to help but hey...

I was surprised about the cheap bus between Amsterdam and London too. Return fares were coming up for 50 or 60 euros but then a whole bunch of 37 euro returns came up.

I wouldn't fancy it myself but plenty do, because the bus fares can be so cheap.

The OP did say "anything to keep the price down so even if it takes me a day to get there or a stop over I would certainly consider it" and he or she does appear to have plenty of time to fit it in.

A $570 fare was referred to but too late. Had it been available, that and the $50 return by bus makes $620. That could save $300 from the other fares mentioned. Worth taking an extra 10 hours each way?

If the fare had been available then yes it would... but it's not so the OP is back to his budget hope he/she manages to find flights within the $650 : )

Plenty of options for that price or less, if you book early enough you can go for £1 on Megabus, although no chance of that for the OP now.

Coach travel to Paris, Amsterdam and Brussels from £18 one-way // National Express Coaches

Cheap bus and train travel in the UK, Europe and Ireland | megabus.com

HTH.