Nowt wrong with 2 strokes so long as you feed them the correct petrol/oil mix and obey the instructions in the Rotax users handbook. They are basically simple engines with less parts to go wrong, therefore cheaper to maintain. OTOH they do tend to use a tad more fuel than an equivalent 4 stroke.
There are some very good microlights available at affordable prices, for example a good Shadow with a 582 should cost you well under £10k. If you train on a C42 you will need an hour or two with an instructor to do a type conversion because the handling is different, especially on the ground where you have to steer with the heel brakes.