To find lowest fares on Ryanair select the "Book now" option. Then tick the
"my travel dates are flexible" box. This service was unavailable for a while but is now restored.
I picked a random date April 22nd. DUB/LGW one way.
Skyscanner shows fare with Ryanair €22.48 including tax.
Ryanair website fare €10 including tax.
Best to check around!