One of my Party member wants to play a Gunslinger. Looking at the price list and taking into account that he has an average of 135 gold I am wondering how he is able to afford a gun on low levels.
Gunslingers start with a gun at first level.
This is granted by the Gunsmith class feature:
At 1st level, a gunslinger gains one of the following firearms of her choice: blunderbuss, musket, or pistol. Her starting weapon is battered, and only she knows how to use it properly. All other creatures treat her gun as if it had the broken condition. If the weapon already has the broken condition, it does not work at all for anyone else trying to use it. This starting weapon can only be sold for scrap (it’s worth 4d10 gp when sold). The gunslinger also gains Gunsmithing as a bonus feat.
Plus, she can craft her own firearms and ammunition using the Gunsmithing feat gained for free.
Crafting Firearms: You can craft any early firearm for a cost in raw materials equal to half the price of the firearm.
Crafting Ammunition: You can craft bullets, pellets, and black powder for a cost in raw materials equal to 10% of the price.
If the Guns Everywhere alternate firearms rule is defined by the GM, then crafting them is much cheaper, going for 10% of the value listed on the tables:
Guns Everywhere: Guns are commonplace. Early firearms are seen as antiques, and advanced firearms are widespread. Firearms are simple weapons, and early firearms, advanced guns, and their ammunition are bought or crafted for 10% of the cost listed in this chapter. The Gunslinger loses the gunsmith class feature and instead gains the gun training class feature at 1st level.
While you can get a gun from the gunslinger class for free, you can get a better gun from the Wizard class or Battle Host Occultist Archetype for free, and then multiclass thereafter. For characters looking to make use of the ridiculously expensive but entirely nonmagical firearms in the Technology Guide, this is the way to go.
Wizards who select a bonded object begin play with one at no cost. Objects that are the subject of an arcane bond must fall into one of the following categories: amulet, ring, staff, wand, or weapon. These objects are always masterwork quality.
A wizard can add additional magic abilities to his bonded object as if he had the required Item Creation Feats if he meets the level prerequisites of the feat. For example, a wizard with a bonded dagger must be at least 5th level to add magic abilities to the dagger (see Craft Magic Arms and Armor feat) ... The magic properties of a bonded object, including any magic abilities added to the object, only function for the wizard who owns it.
At 1st level, a battle host forms a supernatural bond with a specific weapon, suit of armor, or shield. This selection is permanent and can never be changed. The bonded item is masterwork quality and the battle host begins play with it at no cost.
The bonded item is immune to the broken condition for as long as the battle host lives. If a battle host dies and is restored to life, the bonded item is also restored if it was destroyed. Any magic powers associated with a battle host’s bonded item function only for the battle host; in the hands of anyone else it is only a masterwork item.
(note that this ability, unlike the Wizard's, allows you to choose a weapon or armor made of a special material or materials)
Furthermore, while the gunslinger class has access to some interesting or useful features (Gun Training, Some Dares, Some Deeds), it's often a fairly weak class for a firearm-based ranged combatant. Rather than multiclassing into Gunslinger from Wizard you might want to pick a class around the specific combat style you're looking for (e.g. Wizard for a sniper, Paladin for a kick-in-the-door machine gunner, or Ranger for a dual-pistols style character) and multiclass into that instead. You'll have to spend a feat or archetype on Exotic Weapon Proficiency(firearms), but you'll get better stuff overall, usually.
In addition to the above, traits can help. If used in your campaign, Pathfinder characters get two traits by default, and there are two traits for gunslingers on a shoestring to consider.
The first is Rich Parents. Rich Parents increases your starting wealth to 900gp. That's enough for a small secondary firearm; just how good of one depends on how common firearms are in the campaign setting, as mentioned by ShadowKras.
The second is Just Like New. Just Like New reduces the attack penalty of broken firearms to -1 and allows you to fix them for only 150gp, instead of 300gp.
Those two traits, combined with the Gunslinger's gunsmith ability, mean that you could start with a masterwork firearm at level 1 and have 750gp left over for armor, ammo, and supplies.