I have the following input without any form around it:
You need to use the $$ function which returns an array. There are a couple of ways to use an enumerable result.
If you know there will be only one matching element then use this:
$$('[name="tb_website static"]').first().value
If there are more than one input (which is valid HTML) then this gets an array of values:
$$('[name="tb_website static"]').map(Form.Element.getValue)
(By mapping through Form.Element.getValue - aliased as $F - it better handles browser differences and non-input elements that don't store their value in a value attribute)