Hello! Has anyone ever researched the difference in cost for adding bags after booking as opposed to at the time of booking? Is it a set % or does it vary wildly?

with ryanair or wizzair , you should always add lggage during booking

in my reent cases ; the difference was around 30/50%

That is what I suspected.

I have seen a flight I 'might' take - only �15pp at the moment but I was thinking at �15pp I don't mind if I end up forfeiting the ticket cost - but If I have added on baggage etc to make it closer to �50pp I would be more annoyed if I ended up not taking the flight...

Well it depends on the probability you'll actually fly the booking doesn't it!

I've used �20 Ryanair bookings as backup to "posh airline" flights, a few times, when I absolutely have to get to the destination that day (for example positioning flights before an expensive long-haul itinerary). I reckon in the long run I'll probably use about 10% of the bookings I make like this (it's not happened yet). I therefore don't purchase baggage or any of the other stuff that makes it more civilised - on the principle that financially I'll come out ahead over time this way, and if I'm ever in the position of *needing* the Ryanair "backup" flight I've booked, I'll be jolly grateful for the opportunity to pay �200 for my bags/seat/etc and actually reach my destination.

Very true!