yep, get a silicon rtv molding material to make the mold.
(no mold release is needed with silicon)
Most hobby stores (ie. hobby lobby) sell kits from alumilite that would work great for this.

and if you get crystal clear casting resin you can make all the clear parts you want. (not sure about whats in that flower vase material but it might yellow when its exposed to the sun for a while)
regular crystal clear resin has inhibitors in it to slow/stop this from happening.

typically there is tons of stuff on ebay for this
or check out alumilites site for info/materials.


We have used alumilites stuff to make prototypes of molded parts at work with no problems. depending on the material it helps to prewarm the mold in an oven because most casting resins are heat set.