Need to guarantee 99.9% network uptime for ~50 computers. Is WLAN feasible?

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http://serverfault.com – Our current setup in our office uses a single router with 13 computers connected via the Ethernet. We are out of free ports and we need to support 30-50 computers. We need to guarantee at least 99.9% (network) uptime for these computers. All of these computers have WLANs in them. In order to avoid a big hassle with the 30-50 cables, we are wondering if we could use WLAN AP instead. Is reliability/uptime achievable with WLAN APs? Are WLAN based solutions more expensive than normal routers? (HowTos)