First off, CONGRATS!!! This is a great accomplishment!
I would first let both mom and mother-in-law or close sisters know that you would like to have a small, but special anniverary party and that you would love even more to renew your vows. I would suspect that they would be more than willing to help out. Make a list of those things that you can't live without, like the ceremony itself and those things that are not very necessary, like the old, the blue and something new. If you really want to renew your vows, you will definitely find a way to not only have it, but stay within your budget. My husband and I initally got married in the court, but 5 years later I wanted to get married in the church. It was so simple that it was inexpensive, but absolutely the most special day. What made it very special was the ceremony and having my family and close friends there. My splurge was having a singer at the church singing all my favorite songs. We had a small party afterwards that was given by my parents and in-laws, but we just had family made food items on the list, so it was a shared cost and not much.
As far as your little lady, she is turning 6 and the most inexpensive party for her would be a sleep over. Have her invite over her close 3-5 friends and let them enjoy a night of singing and dancing to Hannah Montana. Buy a couple of pizzas, have some popcorn on hand so that they can watch a favorite movie and for the morning, make some french toast. She will absolutely love it and have the best fun. Remember it is all about her, so this night will be all about what she wants and she will love the attention. Just don't forget to let the parents know what time to pick the kids up in case you have plans the next day. I must warn you, these nights make mom pretty tired the next day, but it is worth it seeing your little one on cloud nine.
Good luck!!! Let us know how it all goes.