Ryanair 'first bag charge' goes up £10 to £30 per flight next month.
You failed to mention this is the 'at airport' price. Also any flights booked prior to 1st October will be able to take advantage of the current price (£10 each way for a 15kg allowance)
The online price is £15 per flight, so it will be increasing from £20 per return trip to £30.
As you know I fly with them regular, and the carry on baggage allowance has never caused me a problem.
I've had a look at a couple of the other budget airlines to compare costs;
Easyjet charge £16 for a checked in bag booked online (5kg more allowance) - but on another note if you wish to buy Speedy Boarding with Easyjet this will cost you £8 more than Ryanair.
BmiBaby charge £21.98 for a checked in bag booked online (3kg more allowance) - However BmiBaby don't give you the option to then check in online, so you will have to queue at the airport. (And pay £10 for doing so)
To look at a comparison, I am going to price up a flight from East Midlands to Malaga with Ryanair, Easyjet and BmiBaby. I am going to request 1 piece of luggage on each flight, with priority/speeding boarding. I will also request payment with a Visa Debit card (NOT Electron). I will also select Ryanair flights that are not on offer with free taxes etc to make it as fair as possible.
Dates of travel: Fri 16th Oct - Tues 20th Oct
Ryanair: £121.71
Easyjet: £112.80
BmiBaby: £180.44 (*BmiBaby do not offer priority boarding, their equivalent is pre booked seat @ £7.99 each way)
So EasyJet is approx £9 cheaper compared to the next cheapest (Ryanair) on the above options. You will however have to queue to check in for the Easyjet flight. Had I compared a like for like with one of Ryanair's offer flights, Ryanair would have been approx £40 cheaper than Easyjet and over £100 cheaper than Bmibaby.