Harrington and Richardson, I believe make a good economical one. Thompson Center makes a very nice one. Good thing about these are you can buy interchangeable barrels for other calibers or shotgun.
Nothing wrong with a single shot they tend to be accurate and make you a more accurate shooter/hunter as you tend to be more critical regarding shot placement when you know you likely have one shot. Though with practice you can reload pretty quickly.
If you're lucky enough to be on private land and can leave your stand up during the off season you can tie an old piece of cloth or something of the sort to your stand. I like to use an old camo bandana that I have. That way the deer get used to the movement and eventually don't bother even looking up when there is slight movement. This may just give you the time to draw your bow or raise your gun without being detected.