1) tell her right away
2) tell her it is NOT costing her anything
3) tell her howmuch it cost
4) tell her what you planned on giving up to afford that cost, and for how long.
5) ask her if there is anything she really wants to buy that you can help her budget/splurge for


This has worked in the past for me, but I usually set this up upfront. This is what I want and this is what I am willing to go without to get it, etc.
Budgets can actually HELP give one an escuse to buy fabric/kilts!

Julie