2D
Sure it isn't a typo to say N -> G is cheaper than G -> N ?
A G-reg Star Annual for a complex SEP is about £2500; on top of that are any mods, plus the removal of anything which isn't CAA approved. An N-reg plane could have a list of things that need removing for the CAA; even trivia like nonstandard wingtip lights.
In an extreme case, the N-reg could (e.g.) have a prop fitted for which the right paperwork isn't available.... it then has to be replaced... £10k