It might be an easy fix. See this video: https://www.youtube.com/watch?v=fayeJXj2njA
It's always a good idea to check on YouTube when things break. So much good info there.
I'm driving 2000 Toyota Avalon with 208k miles, so I'm definitely of the repair it and keep rollin' mentality.
It's doubtful the shift lock is the issue; its purpose is to prevent the selector from being moved at all. It's also doubtful that it's an issue with the shifter.
That you can select reverse, you're probably looking at a burnt out clutch that will require a rebuild or replacement of the transmission, but you could get lucky and it might be something cheap and easy.
If the transmission is done, the cost of repair likely exceeds the value of the vehicle.
Personally, I would not put money into a repair like that unless it was my only financial option. IMO it's putting good money after bad. You're better off taking that sum and buying an equivalent, running vehicle and selling or donating the broken vehicle.
I'm sure you'll get plenty of recommendations here to do it anyway.