From some digging around, I found these rates for Singapore Airlines
What it costs:
Where OnAir is the provider (all A380s and some Boeing 777 flights), US$14.99 for 15MB of data or US$28.99 for 30MB on laptops and US$5.99 and US$9.99 for 5MB and 10MB, respectively, on smartphones.
On newer Boeing 777-300ERs with Panasonic eXConnect, prices start at US$11.95 for one hour up to US$21.95 for the entire flight.
The latter being what Aer Lingus also use. So they don't seem to be pricing above market rates for that service.