I have booked the same flights with Monarch but on a different date, they are very competitive at the moment.
I would seriously advise against leaving your booking until the last minute this year, presently our lates availability is nil.
£150 is a good deal to Corfu at the moment, if you see flights at the that price jump on them as they will only get higher.
The reason you are getting such abnormally high prices for the flight-only's with My travel is that they will be quoting the figure from their Tour Ops system which is not effected by fluid conditions, whereas if u book through the dedicated airline's website you will get the current market price, confusing I know but for example the same flight on
www.thomascook.com (Tour Ops) is £250 whereas on
www.flythomascook.com (Airline) its £157. Its all down to a different systems. Tour Ops will sell a set price, the airline will sell at the current going rate, dependent on the usual factors, date, time, etc, etc.
Its not a rip-off tactic its just knowing to go to the correct place which of course unless you work in the industry or are called Eileen its very difficult to know.