There really isnt a comparison between the two units, go for the 773 its twice the machine. Not to mention the extra aux hydraulic output for attachments. The 743's were tough as nails but they are getting aged despite what the paint looks like. The longer wheel base of the 773 is more solid and less prone to wheelies. The engine is sideways in the 773 making it belt driven to the hydro pump. This is quite an upgrade if nothing else. The inline 743 engine is connected via u-joint to the hydraulic pump. This U-joint is impossible to visually see and maintain. It's probable the single most overlooked, under-greased ( 3 zerks I think) part of the machine. This neglected item will fail when the u-joint finally craps out due to lack of grease. When this happens, the engine will need to be pulled to see how much damage was done. It can break all kinds of expensive things, including the main pump,,. I'm not trying to scare you, just educate to you the reality of what can happen. Even to just replace the u-joint for good measure is labor intensive.
If it's a 2001 and has triangle headlights, it should be a G series machine. If it has rectangular headlights it's a F series built between 97-99. You tend to see a lot of year models not match up with what the are in reality. The electronics on the 773 are fairly simple compared to current machines. I think parts are available just about everywhere. The main controller and RH/LH panels can be rebuilt by a company called Isocell.com. They also have replacement panels. A keyed ignition can be easily replaced with an inexpensive aftermarket ignition. You state the dashboards are a pain, but I'd have to disagree. Sure anything can happen to any part on a machine, but there really isnt a pattern of faulty dashes. The BICS controller can give users problems at times. And it's a pain when the machines runs fine, but the BICS has an issue that won't let you drive or operate the lift arms until the issue if found. Sometimes it's easy, sometimes not so much fun. Obviously, the 743 is simple, if It starts everything's going to work. Does this make the 743 a better option? No way.
It's hard to put a value on the 773 without knowing how many hours and location, whether it has an enclosed cab with heat and or AC. A cab package always added roughly $2500 to any machine vs a non enclosed unit. Since covid, prices of everything have risen for no reason other than everybody's doing it, not just skid steers. But if you look at machinerytrader.com, go to skid steers and find bobcat, 773 you will see the asking prices from around the country. Good luck