The new keypad should fix it.
The entry code is actually stored in the lock. The keypads can have parts go bad that result in sending
the wrong voltage levels representing the digits to the lock.
And yes $600 to open the safe seems very high, especially for a typical gun safe.
I just recently installed a Securam Safelogic Xtreme on my safe. It's both an electronic and mechanical
lock in one unit. It's a little pricey but well worth it IMHO.
Got mine at mbausa.com and had to wait for the slow boat from China on the backorder.
Looks like it's still out of stock and they bumped the price on it by almost $100 since I got mine.
May be hard to find one. You could try ordering directly from Securam or from a locksmith.
https://youtu.be/QO7rP5p17_4
Installation is not too bad, but may be too much for some people to DIY.
Here's a very good video that shows the install.
https://youtu.be/IZdCYjeCuwE