For such a small group, Websense probably is too big.
Many routers provide some blocking...usually by domain name, which requires manual adding for each site you want to block. Given your infrastructure, your best bet would be to look for one of two things:
1. Blocking at the DSL point, which is fairly limited, and the feature set is whatever that manufacturer hard-coded into the router.
2. (Recommended) Find a product that integrates into a proxy server, and configure all your clients to use the server as a proxy. Squid is a freeware proxy, and I know it has plugins for web-filtering. I'm sure there are other proxies, and other addons.
Proxy Solution: Pros:
Single point of management for additions/removals
No need for complex client configuration or licensing
May provide performance improvements from caching web-content
Free solutions available
Scalable if/when the organization grows.
Cons:
May be more complex to configure than client-side tool
Some users may figure how to bypass the proxy, thus bypassing your filtering mechanisms
Steeper learning curve for the admin
Performance subject to server load in some circumstances