Retired007: Getting a really good used tractor takes time (or extreme luck!) I would start by walk-thru of every dealer in handy driving distance and see what is on their lot. That will give you a frame of reference for price and models even if you don't bite on one of their machines. In my experience there is definitely some value to having had a healthy dealer go over a machine they took on trade-in. Whether that justifies the price differential is up to the buyer. Notice I said HEALTHY dealer -- some others will put nearly anything out for sale. A good dealer will check a lot of basics that you won't have to worry about AND even if they do not "guarantee" the thing per se they will almost always help if you get it home and immediately find some glaring issue. They do have a reputation to protect. Second, go to Craigs List and see what is for sale in reasonable radius. Third, go to TractorHouse.com and see what is there (filtering out the size, type and where it is located...) It is a fun thing if you are not in too much of a hurry and enjoy shopping machines.
By the way -- I don't know your situation, steepness of ground, typical grass mowing chores, etc. BUT I had a 6ft JD MX6 hog and at the same time I had a Landpride FDR2572 finish mower. Pulling with a JD4700 48HP (at engine) tractor which was slightly overkill but not all that much. Depends what you are cutting. That finish mower was noticeably more load to pull (esp. on hills) than the hog was. I would say 25hp will run a 6ft hog barely but you really need to move up a few HP. Definitely move up to 30 at least if using a 6ft finish mower. My opinion.