I am trying to do a 10 day trip ..dates are totally flexible.

I see flights from MAN to GIG for under £700 in June July and August

All the flights go through EWR. I would like a 4 day stopover in EWR so I can take a side trip to PTY.

I have tried every posible way to do this i.e MAN -PTY-GIG-MAN
MAN-EWR-GIG with 4 day stopover so I can fit in (EWR- PTY-EWR) then return GIG-MAN. The problem is the flight excluding the side trip to panama shoots up to £1500 region.

How can I take advantage of the low MAN - GIG fares and have a stopover in EWR.

All help more than greatfully appreciated..

Also is there any search engine that can help me find the cheapest way of having a stopover if I am flexible on days