Zuku tripple play 8Mbps will be good for you. That will average a single comp to 100kBps or 800kbps per comp. Most browsers need atleast 40kBps to draw their pages fast impressively. A 5MB file will take 50sec to download on any comp when your connection is working optimally assuming all comps are downloading that same file at the same time. Otherwise it will take 7sec.
The additional TV offer that comes with it can serve as entertainment if you can't afford to serve your customers with drinks
The entire package is 4k per month.
If you are feeling adventurous you could go with the 20Mbps zuku tripple play. That one has mad mad! speeds, your connection will be idle for most of the time because of how fast it will be responding to requests drawn by your end users.
It will set you back 8k monthly.