Good Morning AlisonD,
How much currency you take depends entirely on the amount of items which you think you will buy. USD cash is this best currency to take, but you will need to check your travel insurance policy to check the amounts which you are insured for.
You may be able to order Costa Rican Colon from some larger currency exchanges centres.
We do not generally recommend the pre-paid cash travel cards because they charge you for every transaction you make and can be difficult to top up while abroad and some expire if you do not use them every 3 months.
I hope this helps.
Kindest Regards,
Amy