If you want to get out on the water this year, you'll probably have to row a single. Like bikes, they are flying off the shelves now that some restrictions are being lifted. In trying to figure out what boat will be best for you, decide how much money you want to spend, what kind of conditions you'll be rowing in, and whether you want to race or simply have a way to get out and row.
Used boats are like used cars - what they cost will depend on their age and condition. I always recommend seeing and trying out a boat before buying, as different boats fit people differently. A boat that has been damaged and repaired doesn't have to be a deal breaker, but inspect the repairs and find out if it has added weight. If it has been rowed in salt water, check for corrosion. Make sure the boat will fit your height and weight and ability level.
If you only have a big body of water on which to row, you may well be better off with an open water boat, such as a Maas Aero or 24, a Peinert Zephyr or Dolphin, an Alden Star, or even a rigger mount you can strap onto your Stand Up Paddleboard. If you're new to sculling and/or rowing a single, you won't need as much of a learning curve to feel comfortable in these options.
If you want to use this opportunity to finally make the switch to a single and start racing, do your homework. There are many racing boats out there with prices ranging from $6,000 to upwards of $15,000. Empacher, Filippi, Fluidesign, Hudson, Kaschper, Peinert, Pocock, Resolute, Swift, WinTech, who did I forget? Again, ideally, I would recommend trying any boat before you buy. What your friend has and loves may not be the right boat for you.
Find a boat that fits you. If it's too big, you'll feel like a cork bobbing on the water; too small and you'll have trouble getting the blades out of the water. Most boats have weight ranges for which they're best suited, and they can be pretty wide-ranging. Height of the oarlocks can also be adjusted, usually without too much effort. Ideally you want the oar handles to be just about bra height/heart rate monitor strap height when sitting at the finish. If the oar handles are too high, you can move spacers from below the oarlock to above. If the handles are too low, move spacers from above to below.
For first-timers, one common mistake that can make sculling almost impossible is inserting the oar into a backwards oarlock. Often in sculling, unlike sweep rowing, there is no backstay, allowing the oarlocks to turn 360 degrees. If the oarlock is turned towards the bow, the pitch will be totally off, making it very difficult to clear the blade at the finish. Oarlocks must be turned towards the stern.
When adjusting the foot stretchers, look for your hands to almost clear the body at the finish. Not enough room and you'll find yourself getting stuck, too much and you may finish behind the body, a weak position but also one that can lead to a dunking if it gets caught back there.
Let the blades skim the water when you start out
If you're new to single sculling, the best thing you can do is relax. Don't fight the boat, don't grip the oar handles too tightly, don't allow yourself to get stiff. The more you relax, the better it feels and the more you'll relax. Allow the blades to skim on the water initially as you figure out the balance. Aim for level hands and a level blade depth throughout the stroke. There doesn't seem to be any need to rush, so take your time and develop some good early habits that will bode well for the long run.