How to thank dad for accepting my lifestyle?

[Sarah]

When I was 6 (I'm 23 now) my parents divorced.My dad remarried when I was 9,my mom also is remarried.As a teen I finally accepted I am a lesbian and decided to stop fighting it.I told my mother and she rejected me.My stepdad is a minister and he said that he could not have a 'sinner' in his house.They spoke with my dad and decided I would go live with them.They were totally accepting and loving to me.I could talk to my stepmom about things I couldn't talk to my Mom about.When I finished high school they helped me through college and always told me how proud they were of me.I finished school last June and got a good job as a nurse.I've been with my girlfriend since I was a senior in high school,almost 6 years,and she is totally accepted by my Dad and stepmom.They include her in all of our family gatherings and they are totally comfortable with our relationship.My mom only spoke to me twice in 5 years,just to ask if I gave up this whole 'lesbian' thing.My dad's anniversary coming up and we would really like to do something great for them for accepting me and my partner.They don't make a lot of money,so I would like to give them something they would never get for themselves.Any good ideas?