Roget's for a few dollars, for sure. There'll be competing copies by multiple publishers, which should drive the price down. (Sorry, just saw the qualifier 'second-hand store'. That would be much cheaper.)

I'm not entirely certain expanding your vocabulary was what Alex had in mind, though. My impression was that he was advocating using your current vocabulary differently (if this is a misimpression, please correct me, Alex).

My old creative writing instructor used to say, "Don't tell; show." Although he never expressed an aversion to adverbs, 'showing' does tend to reduce their usage. To give you one example: "A week later, Kate found herself fidgeting from foot to foot in her doctor's office, wondering how much her hospital gown was revealing." Okay, that sentence had problems of its own, adverb or no adverb, and may not at all convey what you intended in the scene, but it did remove one adverb (at a cost of doubling the sentence length!).