According to coinmarketcap.com the market cap of the XRP is currently $606,293,939. However, according to a post in xrptalk.org 90.91% hadn't been moving as of the 17th of August. This would calculate to a liquid market of approximately $55Mio.
As more than 40% of the total XRP are still announced to be spread into the market, the value of XRP is bound to strongly fluctuate and should at this point be considered unsuited for storage of wealth.
Unlike the question suggests, the Ripple network is connected to the Bitcoin market and therefore can be used to pay at any shop that accepts Bitcoin payments. The source code of the server software has yet to be released though, so that even impartial parties suggest to wait before pouring value into the market.
Arguably the market cap of Ripple doesn't only derive from the value of XRP, but all different currencies that are being moved through the ripple network. Unfortunately, I have yet to find numbers on other liquidity and balances in the system.