You lose one port on each for its network connection, so if you use 8 port you have 7 available -- to connect 50 devices you would need 8.
Look at bigger switches, the 16 or 24 port are pretty reasonable. You could get by with 2 24 port and an 8 port.
If you want consumer grade unmanaged switches look at TPLINK
and Trendnet, they work as well as other inexpensive brands.
Do you need gigabit or just Fast Ethernet (100Mpbs)? Personally, I would lean toward spending the extra and getting gigabit -- the inexpensive 24 port Fast Ethernet are around $50-60, while the gigabit are around $120 each.