Maintenance costs are an issue - perhaps someone could give a ballpark figure for what the annual costs on an SR20 are likely to be (used or new?)
I can't speak for an SR20 but the last annual on my 11 year old N reg SR22 was £6.5k having flown 265 hours over the year.
You won't need to pay airways fees if you're flying VFR as a PPL.
I think all UK airways are class A airspace, so you can't fly VFR in them anyway. Assuming you have an IR and therefore can fly in class A, you don't pay airways fees for using them if you're in a SEP such as a Cirrus or PA28.