Well, I reverse engineered a die roll based on the Swashbuckler's starting package. It ended up being 4.2 d4 x10 gp.
For the mathematically curious, I added up the value of all the equipment (90gp) then added the average of the 6d4 die roll (15 gp). For a grand total starting package of 105gp.
Then, I figured that to get the average of a starting gold roll you add the minimum roll to the maximum roll and then divide by two. Then I substituted X for the number of d4s to roll. So, the minimum on the roll would be X x10gp and the maximum would be 4X x10 gp. To get the average, that'd be 25X equals the average wealth roll. Solve for X, that's 4.2 d4 x 10gp for the Swashbuckler. (For fun, I also calculated starting wealth based on the Rogue's and Fighter's starting packages in the PHB. Rogues get shafted, their starting package is the equivalent of 4.38d4x10. Fighters get a bonus, they had 6.04d4x10).
4 or 5d4 x10 sounds right for the Swashbuckler. Rogues get 5d4x10, but they have to buy Thieves' Tools usually. Bards get 4d4x10, and like the Swashbuckler are light armored, light weapon types. Now to convince my DM to give me 5d4 rather than 4d4...