Hello @Nyxie_Rose,
Both the mice concern and the mindfulness about food costs are very valid reasons to not offer food- luckily, there are many other options of things you can offer to your ancestors! 
@Amethyst shared a really gorgeous prayer- the time it takes to read, the breath you use to say it, and the intent of the words themselves are all very heartfelt offerings to share at your altar.
Additionally, I second what Amethyst said about incense- that is a great one to offer! Other non-edible offerings include lighting a candle, a bowl/glass/jar of water, flowers, or other interesting things you find while outside (feathers, stones, etc).
There was indeed a challenge about making offerings and the coven shared some very creative ideas! Here is the link- if you scroll down to the bottom, you can read the experiences and offerings shared by coven members:
I hope you can find the perfect offerings that work for you, Nyxie Rose- good luck and blessed Feralia!
