Personally, I like the 41 long Colt. I just received a Thunderer and a Lightning in trades (I have a Bisley in 41 lc, also). It has a reputation of being a fairly effective stopper.
As an aside, before I get into the Thunderer, my Bisley is rapidly becoming my favorite range gun. Accurate, fairly powerful and easy on recoil.
Another aside: My Lightning was fun to shoot once but is going to be a safe queen. It's a Sheriff's Model and a real pain to load and unload.
Now, as to the Thunderer: As you already know, DA pull is atrocious and SA isn't a whole lot better. While the 1877 have a reputation for breaking, they will hold up judicious use.Obviously, no quick draw, fanning, etc.
They use a different mainspring spring from the SAA, so order one, when you can find it.
Felt recoil is greater than the SAA due to the obviously smaller size. The birdshead doesn't help (My 1878 in 45 Colt is almost painful to shoot with cowboy action loads-smacks my middle finger pretty hard).
Ammo is expensive but so are some reloading components. Brass isn't too bad==I ordered directly from Starline (cheaper by about $10 if I remember right for 250). You will need either a hollow based, soft lead bullet or a bevel base (like a 22 rimfire has). The best place to get them is GAD custom ammo=he has both types, as well as loaded ammo. Western bullet makes them but communication sucks and so does delivery time. Midway has some-very expensive (Montana bullet) and so does Buffalo Arms in Idaho=also expensive. GAD is 2/3 the price. Western Bullet had a messy lube on the bullet. You might want to simply buy loaded ammo (but, it's about $75 a box).
Price really can't be judged without examining the gun. Likely not worth to someone what it would be worth to you. There is a nostalgia (?) or mystique to shooting these old guns. I have several old Colts, a "blood gun" from Iwo Jima, a stage coach company shotgun and some WWI and WWII guns. You always wonder what the history is. Was your grandpa (condolences by the way) a lawman? A cowboy? You never know. After mine died, we found his work ledger from 1918 saying he won $200 at the Calgary Stampede and $100 from the Pendleton Roundup!
GunBroker can give you a good idea of selling prices. Here's mine and the trade values (Remember trade values very considerably from cash values)
My Thunderer:
Trade value: about $1000
My Lightning:
Trade Value: about $800.00