You can find rabbit fur sporrans on ebay for about $30 delivered. That's where I got mine. It looks fine.

You might consider using the money to have a jacket you already own altered to serve as a semi-formal kilt jacket. While there will be many at your burns dinner in formal dress, you will blend in more as long as you have a jacket on. Even a standard vest will look better without a jacket.

Don't let the clothes deter you from going though. I understand the desire to present yourself properly at the dinner but reality sometimes prevents us doing everything we want. Most people will not comment on why you are not dressed formal. If they do, they are extremely rude. Attend and enjoy yourselves.

Otherwise I'd go with the Buzz Kidder for the same reason S4 mentions, it will be more functional on a daily basis than a stiff semi-formal. Forgo the bling bling and choose function.