Gold and silver bullion bars and coins are your possessions and you can do with them and travel with them as you like.
However,
You must declare any amount over 10k on a simple form. You are not (legally) taxed in any way, but you must report larger amounts or you risk confiscation and a visit with local law enforcement.
With regards to "current spot prices/oz" it's as I understand it up to the official questioning you to use their good judgement. I'm sure you would slide through if you had 12 krugerands instead of just 10.
You can gripe all you want about the reporting requirements; one of the reasons why people buy especially gold or platinum bars and coins is the privacy. However, you must understand that like with a lot of things in life, bad people have made things harder for everybody else. A typical way to launder money is to move precious metals around through ports. If you're carrying 50 pounds of gold bullion, it is certain that you will be stopped.
By the way, one of the biggest reasons that gold is more widely invested in than silver is that simply it is more valuable/oz than silver. A fortune in gold can be carried in your pockets, whereas 20k in silver is over a hundred pounds and quite bulky. If you're concerned about travelling with your coins you're much better off selling the silver, and buying platinum or gold, and then rebuying silver wherever you end up.
Also, while I am in no way recommending that you bypass reporting requirements, rhodium is over $6k an ounce last time I checked.