At least four Watchkeeper army drones being tested in Cardigan Bay have been damaged beyond repair, with each one costing almost £6m each.
The Ministry of Defence (MoD) said it is "too early" to say whether a fifth drone, which crashed near a school in Ceredigion last month, is salvageable.
If all five are beyond repair, it brings total losses to almost £30m.
Four of the drones have crashed in Aberporth so far, either on land or in the sea.
Watchkeeper, which is designed to provide "vital intelligence gathering and surveillance for the British Army", is now expecting to cost at least £1.1bn, against an initial estimate of £800m.
The MoD ordered 54 Watchkeepers in 2005 as part of an £847m deal. Originally, it was hoped they would be in service by 2010.
As of November, Watchkeeper has flown for 2,859 hours, but only 146 of those were "on operations" according to the MoD.
Pictures gathered by BBC Wales last month show one of the Unmanned Aerial Vehicles was badly damaged and broken into pieces when it crashed in a field near Penparc School on 13 June.
Ceredigion MP Ben Lake has called for the Watchkeeper's flight path to be diverted away from the school.
"There have been significant concerns," he said.
"A lot of people have raised them with me, a lot of parents in particular.
"They are concerned because they are aware of a number of accidents now with these drones and are asking how safe are they, if they're flying close to the school."
A spokesperson for the MOD confirmed that Watchkeeper resumed flying from West Wales Airport on 17 July following the crash.
The MoD said: "Following a review, it has been concluded that it is safe to resume flying."