Silkcoin [SILK] was at $300K market cap but the market is currently closed because there is a swap going on to the new Silk [SLK]. SLK is opening on Bittrex in 24-48hrs and I think it will blow up. Before SILK was removed from polo a couple weeks ago it was 1600sats. Once it opens on Bittrex it will easily double or triple. So if thats what you mean by "Best coin under $500k" then its an easy one to double or triple.
If, however, your question is more about innovation then SLK is intriguing because it is the digital asset that backs the currency DarkSilk [DSLK] that will also be opening on Bittrex in about a month. Silk adapts to the DarkSilk supply in order to stabilise its price. In doing so, the price of Silk will oscillate and provide great arbitrage opportunities for investors.
More info can be found here:
https://bitcointalk.org/index.php?topic=1601099.0 https://silk.silknetwork.org/I personally know pump groups that are involved and waiting for the market to open so be careful. Even if it gets pumped the ideas and team behind it are legit.