I search for the internet and try to buy ASA5505-BUN-K9 or ASA5505-SEC-BUN-K9 . Are those two firewall products can meet my requirements ?
In my opinio the cisco ASA 5505 works well for 100 users. Just make sure you got the required license needed for the inside users i would suggest get the unlimited license for future users. Also plan ahead for licesing if they need any feature set like dmz and vpn connections. Cause to enable DMZ is a security plus license is required.
Account for growth. I would probably peek at the 5512x if I were you.