No, a L-39 and similar aircraft will not fit your purpose. Mainly because they are classified as "Exhibition Class" under Experimental and as such are issued airworthiness within a 600nm radius around home base with further travel only on special request. Yes, there are quite a few demil aircraft, but mostly flown by enthusiasts and not for frequent travel. Further yes, there is a complicated way to get a waiver from the 600nm restriction. There is a vital group flying these birds and especially the L-39 has big fan boys. They are comparably affordable and good ones start as low as 200k, with at 400k typically equipped with bells&whistles. They are nice trainer and after the 500 hours plus training flyable by the ordinary PPL pilot (of course, what do you think the airforces do - they put students in there with 50h tached and at 500h these defend you country in an Eurofighter).
Your fiance most probably won't like such a bird as it still is designed as a figther trainer and IS uncomfortable. Operational costs for a L-39 would be around 1000/h, about 3000/h with maintenance, so comparable to high power GA. As it is Experimental reg'ed flying across borders is quite some paperworks.