Choosing the right search terms for your rental
You don't need keyword software to find the terms that matter. You need to think like the three or four kinds of guest who actually book places like yours.
Start from who books, not from what you'd like to be found for. A lakeside cottage might get booked by families wanting a quiet week, by couples wanting a short romantic break, and by small groups of friends wanting a base for hiking. Each of those searches differently: "family lake house with dock", "romantic cabin getaway", "group hiking cabin rental". Write down the two or three searches each type of guest would realistically type — not words you want to rank for in the abstract.
Use the free tools you already have: type a partial search into Google yourself and read the autocomplete suggestions and the "related searches" at the bottom of the results page. These are real, current searches other people are typing, not your guesses about them.
Prefer specific phrases over broad ones. A page trying to compete for "vacation rental" is competing with every listing marketplace on earth. A page built around "quiet dog-friendly cabin near Asheville" has far less competition and matches almost exactly what a smaller number of people, who are a very good fit for your property, are actually typing.
Once you've settled on the two or three phrases a given page should serve, use them naturally in the title, the first paragraph, and one subheading — not stuffed into every sentence. A page that reads naturally and happens to contain the right words beats a page that reads like a list of words.