Alright, so, I'm really new to this forum and I really love this game. I've been a long time lurker for a good few years but I've never really joined until now. Short life stories aside, here's what I've got in mind.
At present, I'm in the middle of developing a lot of new races for a new world setting I've got planned. One of the inhabitants of said world is a race known as the "Lesaar" which may as well be Lizardfolk with a few extra trimmings.
The Lesaar have a +2 to Strength and Intelligence, but a -2 to Charisma. Their racial qualities look a bit like this.
Slow (-1 rp), Bite (1 rp), Claws (2 rp), Greed (1 rp), Natural and Improved Natural Armor (3 rp total), and then, I have this really strange racial quality that I made myself. Unlike a lot of folks that I know, I actually like Gnomes and the "Obsession" racial quality always really interested me and set a person up for really decent roleplay opportunities when the time actually came. That said, I wanted to throw that at this new race, only... with a little more oomf.
For that exact purpose, mind you, I created "True Obsession"
True Obsession (3 Rp?): At first level, a Lesaar must pick a Craft skill as their true obsession. A Lesaar may not pick Spell craft for his True Obsession. A Lesaar may not use Spellcraft for the purposes of creating magical items. When a Lesaar picks a Craft skill as his true obsession, he gains a +4 racial bonus to that craft skill. A Lessar may not use any skill but the one he chose as his True Obsession for the purpose of crafting magical, or mundane items.
Just looking at it, I kind of enjoy the idea, and I can already see my more "Crafter type" players cringing a bit at the idea of sealing spellcraft off for the purposes of crafting, but the Lesaar aren't actually supposed to be wizards, even if they could function very well as one given their stats and setups.
The Lesaar, as a race, are built around making a community full of guilds that all do one thing really really well. Their offspring are allowed to focus their obsession on something else, but their elders will often suggest they keep with what the family is doing.
Story aside, what I'm mostly curious about is what do you folks think about that racial quality? Is it 2 points? 3? 5? I can't really place it.
I'm just going to bump this once, because I was foolish enough to post it at 5 AM, if that's alright.
I probably wouldn't lock out all other crafting. Instead, they take -2 when crafting with any other skill (including Spellcraft) and you price it at 2 RP.
At the least I'd make it a -4 to really drive the point home.
If it was me, I'd stick with the standard obsessive same as the gnome, and just have societal pressure to stick to only one craft be flavor, not mechanical.
I think you are overestimating the amount of effect such a trait would have on role playing I would expect players who choose this race will only have a single craft skill, and you won't ever see the downside, and players that want more crafting won't choose this race, so all the flavor becomes invisible (and mechanically doesn't matter) during game play.
Indeed I think not having it be built in mechanics on the race actually opens up more role-playing possibilities, the character that is an outcast because he studied both alchemy and leather-working for example.
I tried creating some races a while ago, as I got my hands on te Advanced Race Guide.
Most of the time I came up with something similar, like what you plan for your Leesar. It's much to narrow to be a race description. To check that, youcould simply come up with a Leesar Bard, Fighter, Ranger, Sorcerer, etc. and see if it works.
There is no in game reason for a race not beeing able to use Spellcraft as written in the rules.
As for building the race I would stick to things already around, for it is much easier to put a number on that. To achieve your goal, you could add skill focus as a bonus feat, with the limitation on craft skills.
To reach your goal it would additionally make sense for them to have Master Craftsman, but you couldn't possibly hand that out at first level, and thats your strong hint, that what you're planning to put together is to narrow. Everything that can't be set and take effect before you choose your 1st class level is propably placed wrong in a race desrciption.
Maybe if you split it up in a race and a Racial Archetype?
Just my two cents worth.
True Obsession: Choose one Craft skill [no need to mention spellcraft, Craft skill is sufficient definition]. Gain +2 racial bonus to that craft skill, and the Master Craftsman feat as a bonus feat (ignoring prerequisites) for that skill [total bonus: +4]. All other Craft skills, as well as rolls to create a magic item using Spellcraft, take a -4 racial penalty.
Price: 1 RP, IMO. Craft skills are useless and Master Craftsman is a terrible feat.