I have seen a very wide range of prices on Tefillin. They range from around $150 to well over $800. Is there some greater merit in the more expensive Tefillin?

A more expensive Tefillin alludes in most cases that they are on a higher level of Kashrut and Hidur – beauty. That is a Mitzvah on its own – to beautify the Mitzvot. Therefore it's not the more expensive Tefillin you are looking for but the more kosher and more Halachacly beautiful. My strong advice is that if you can afford it – don't buy a cheap pair of Tefillin.