I don't know what your budget is, but have you thought of a zoo membership? Our 2-yo loved the one that a couple of her grandparents gave her. The nice thing is that under 3, they are free so you can get one of the smaller packages (1 adult, 1 adult + child, 2 adults, etc.) and still take her for free. Also, with a paid membership, you can take up to 5 people with you for 1/2 price. So, if you got the 1 adult + 1 child membership, you could take both girls all year long, then if dad joins you on the weekends, he's half off! :-) The nice thing is you get a year of memories and adventures without a huge cost. And, you don't feel guilty for only hitting part of the zoo each visit - it actually adds to the fun because you can pick which animals to see each time.
As for the party, I'm really big into going with what your child is interested in. Our little girl LOVES books so we had a bookworm party for her 2nd. I made a 3D cake and custom invites. Because I didn't buy a pre-made theme (e.g. Backyardigans, Disney stuff, Elmo, etc.), I could pick out whatever decorations, plates, etc. I wanted (and save money). The best part is that most people bought her books (she ended up with 30+ new books) because of the theme. We didn't have a house full of new toys, and it made it easy for everyone who wanted to give her a gift.
Also, to save money, think of having the party at a park, your or a friend's backyard (weather permitting). It's a great way to have a cheap outdoors theme - you don't even need decorations. You could make cute bug (ladybugs, bees, etc.) and/or flower cupcakes, or super-simple "dirt cake".
One last idea is a garden party. Instead of toys, suggest that everyone bring a small plant so you can make an indoor (or patio) garden with her. Things like herbs or annuals would be great. Just some quick ideas. Have fun!!