Hi there,
You are correct in your view that the lower payments will not justify the fees involved.
Imagine it like this, a 3% erc, lets say you go for a 2 yr deal, that deal needs to save you 1.5% per year just to cover the 3% erc (crude example, but makes the point).
The final question is an interesting one and you would need to do a calculation of total cost for both options. Also remember that if you add the fees to the mortgage you will be paying interest on them as well.
Essentially, there will be a point where if the new rate is low enough, it would be worth your while switching, however I very much doubt you will find a rate low enough to justify all of the fees.
If you want a more detailed chat, contact an indepepndent
mortgage broker.