I'm thinking Strawberry Shortcake and Honey Pie!
For your daughter, you can order a Strawberry Shortcake costume online. Here are some photos (I found using Google for reference).
I think it would be very cute
Reference images:
Click to view Strawberry Shortcake
Click to view Honey Pie
Strawberry Costume:
Price: $23.20 (Wig is an additional $10) plus shipping, or free shipping if you have Amazon Prime (you can get a free one-month trial, but you'll have to remember to cancel it before you get billed).
Strawberry Costume on Amazon.com
For your horse, you'll have to paint him to be golden, but the dapples may work for him since Berry Pretty Ponies seem to have dapples. And buy some flowers to decorate the mane next to the ears and a big green bow for the tail, plus a saddle blanket (pink with white trim if possible).
Here are some product suggestions for coloring your horse:
Show Touch Up Paint About $11/color plus shipping.
You'll probably need Sorrel (for the body) and Palomino (for the mane) and maybe the white, too if you want to paint white areas also.
Total price if you buy everything should stay under $100 for sure, and may even include shipping
To me, that's an affordable price to pay for costuming 2 bodies. But I don't know what your budget is. Hope you like my idea. You don't need to use it, though. I won't be hurt