Your gearbox will be either an FS5R30A or an FS5W71C. Variations depend on country, but typically the VG30E model in Australia had the FS5R30A and all other models had the other one, although with different ratios (so in other words, I'd need to know what engine and what part of the world you're in to identify the gearbox exactly). There's a table on page 142 of the service manual listing the different models and ratios for each.
Typically for Nissan, the FS5R30A box also seems to have been used in the 300ZX, Nissan Skyline R32 GTR, Patrol GU Y61 and the ZD30 Navara D22. The FS5W71C seems to have been used in the 240SX, 240Z, 280X, 280ZX.
You can buy refurbished boxes for just over the $2K mark, but rebuild kits are < $200 - would that suit?