I have sumps, 40g with a hob filter and a small AIO. I was just thinking the other evening about what I would do if I were to simplify things and only have one tank and I decided a decent AIO would be my choice. Its just simple and easy. I'm not a gear head and don't find a skimmer, reactors, roller, controllers etc to be necessary so that help keeping it simple. A tank large enough for a few cool fish and some nice coral would work for me. I would probably just do a larger version of my IM20.
No mechanical filtration other than some floss when I clean the glass or blow the rocks off. Jebao return pump, heater with an inkbird, ATO and a couple of powerheads, rock and water. EDIT: A good light also and probably the most expensive item in the tank.
I used mostly stuff I had here except the tank and light so my cost was minimal. I imagine as
@rtparty said $2k would probably get a nice sized AIO. Maintenance is so simple that cleaning the glass is the hardest part. I rarely even do water changes on this tank. I pour in a little AFR in each morning and fill the ATO container once a week and spend the rest of the time fussing on the other tanks because I do like to fiddle with things.
Pic from this morning.