Refractors split into two products with very different prices, and choosing between them is really a choice about what you will point the instrument at. Getting that clear first makes the shelf much smaller.
For planets and the moon
A long focal ratio achromat or a modest apochromat. Both give sharp high contrast views of bright objects, and at f/10 and slower the colour fringing of a simple two element objective is faint enough not to intrude. This is the traditional refractor use and the cheapest way into the design.
For deep sky photography
A short fast apochromat, which is a different product at a different price. William Optics prints $498.00 for its cheapest, and that is the entry to the category rather than its middle. The money buys specialised low dispersion glass and a field clean enough that a camera cannot fault it at the corners.
For faint visual objects
Not a refractor, honestly. At any price a reflector gives more aperture, and faint objects are a contest about light grasp. A 6 inch refractor is a large expensive instrument and a 6 inch reflector is a modest one, and on a galaxy they show the same thing.
What to check before buying
The focuser, which on refractors carries a camera and must not sag; the dew shield, since refractors dew readily; and whether the price includes a diagonal and rings, which on premium instruments it often does not and which add up quickly.
Questions people ask about telescope
What is the best refractor telescope?
For planets, a long focal ratio instrument of modest aperture. For photography, a short fast apochromat, which is where most of the price of the category sits.
Are refractors good for viewing planets and galaxies?
Excellent on planets for their aperture, and outmatched on galaxies by cheaper reflectors that gather far more light.
How much is a good refractor telescope?
Small achromats start below a hundred dollars. The cheapest apochromat in this index prints $498.00, and that is the bottom of that range.