That sounds like such a fun costume! And should meet your requirements - you already have the Fjord! and the basic tack!

The horse tack shouldn't be too hard, and depends on how crafty and quickly you can pull it together.

Saddle Cloth:
- Use a large piece of fabric (2 yards at least) to drape over a regular saddle pad
- Or a Purple Saddle Blanket, or Purple saddle pad
• At a fabric/craft store, grab some Trim - example
- Check out the Dollar store as well for some budget ideas. Paper might work for this as well
- you can add in the little tassels to the corners

Breast Collar
- Cover in dark fabric or if you have a dark wide leather one (or can borrow like a western one) - add some of the leaf trim.
- Could use Gold Puffy Paint

Depending on the time (and skills) - sew everything together, hot glue it together, or if you're out of time, staple it on! (totally have no experience doing that -.-)

The harder part is going to be Hans' outfit.
- A Blue Button Down
- Purpleish/Red Tie
- Purple Breeches
- Black Belt
- White Gloves
- White Jacket (check out thrift stores! - anything from leather to blazers) | if you want to add the black accents, you can cover/pin black fabric pieces on top of the jacket
- Black tall boots or half chaps

The Hair / Helmet
- Grab a large wig and glue/pin to a helmet
- Glue/Style on some sideburns

Just note that the fabric and extras are going to be on the expensive side - if you can re-purpose something you already have, that will save you time and money. Thrift stores can give you some good deals too. They might have a Hans costume (or look-alike). With not a ton of time to prepare, you might have to make concessions on quality or extras.

- Avoid satin or slippery fabric for the saddle cloth! You don't want the saddle slipping while going over a fence!

It should be do-able though! And you'll have to post pictures!