If you look at eBay then you can find many high quality close-up lenses at reasonable prices. Some companies, like Nikon, made both 2-element higher quality models and single element models. Even the old 0, 1, 2 single element Nikon models do quite well with a 50/2 or 50/1.8 if you stop down. The 3T/4T/5T/6T models are no longer made and can be expensive when you find them. Both Konica and Minolta made 2-element close-up lenses of very good quality. The Konica models are mostly 55mm size. The Minolta ones came in 49, 52 and 55 with the 52 and 55 sizes being more common. Topcon's 2-element close-up lenses are usually found in larger sizes like 58 and 62. Sigma made some nice Achromatic close-up lenses. A few of the larger size ones will only mount with a lens that has a front bayonet mount. Asahi also made some 2-element models. Consider finding step-up or step-down adapter rings if you find a nice close-up lens at a good price but in the wrong size. Some companies made fractional diopter close-up lenses. These are usually found in large sizes and can be helpful in getting long telephoto lenses closer. Canon made and may still make some very nice 2-element close-up lenses like the 250D and 500D models. The problem is that they have become cult items and can be expensive. Some people attach a reversed 50mm lens to the front of a 50 or longer lens for more magnification. This is done with an adapter ring which has a male thread on both sides. You can buy these or make them. A good reference for close-ups is the Manual Of Close-up Photography by Lester Lefkowitz. Old copies are available online.