Flying to Lelystad below 1200 feet is no problem. If you're happy with a cross country flight at that altitude then you should have no problems, there are only two really tall towers that you might encounter and the elevation stays below 50 feet all the way. Hilversum is cheaper than Lelystad I think but it is a small grass airfield with some strategically placed trees. Make sure that you're happy flying in and out of fields like that and that the aircraft will fit in there, runway length-wise. Otherwise Lelystad is the better option. You might also consider Midden-Zeeland (you'll pass it anyway if you cross the border from Belgium near the coast).