Pre-Dominiom war when everything is pretty chill. Starfleet kinda seems fun until you realize that you have to basically do military training and all this bullshit to join and then you gotta go die in space half the time. I'd maybe just try and get a runabout or the equivalent and just sorta wander around with some pals and look at totally safe and previously explored space things. I would also open a Volcel Precinct on Risa.
There are also plenty of times that a shuttle craft not being warp capable is crucial to the plot, ds9's The Sound of Her Voice for example. I'm going into ship manual quasi canon stuff but the enterprise D had like...a LOT of shuttlecraft of different variety. Later on in late tng early ds9 the variety would be parsed down to a standard none warp capable shuttlecrsft and a warp capable runabout which was larger and had greater warp capacity than the few warp capable shuttles starfleet had beforehand. So, if you're not in starfleet or something like thar, chances are your shuttle isn't breaking warp.
I was honestly thinking outside the Federation would be more likely for the shuttle to be warp capable, because not having a huge ship around would make it a necessity. Like the Enterprise can afford having ships that are practically dinghies, someone selling a civ shuttle would be selling to people without that luxury
The federation isn't just Starfleet, remember. So it's sorts the difference between military and civilian tech minus the capitalism. The cutting edge cooler stuff being only used for certain ships and the tried and true being used for the majority of the fleet has been seen due to the fact that production wanted to reuse old ship models. I'd wanna stick to federation space and not too far from backup cause I've seen the show and know I could get attacked by a Greek God or Lincoln.
It does seem like any random asshole can get a warp capable ship if the plot needs it though. Can't be too hard to come by. I was also considering general living space too, a shuttle is like a trailer that you can't leave. A runabout or something like that has more room to.
We don't really see civilian ship manufacturers do we? It would seem most options for federation citizens are federation built or made outside the federation. That's why I assume they would have warp drives, you need to be offering _something to buyers. Business would need to be super localized for dealerships if you are selling only single-system crafts. Not out of the realm of possibility, but even just an emergency warp drive would make sense. People buying a private vessel for themselves are likely willing to shill out the higher price a warp drive and associated upkeep requires.
Trek doesn't really have much in the way of in-atmo craft like Star wars
There's stuff like the Vulcan Science Institue and other ventures that fall under federation jurisdiction or 'funding'. Lower Decks had that recruitment day episode that shows a whole bunch of the space weirdos with spaceships are part of some kind of guild or whatever.
Transporter technology and the fact the average Starship can depopulate a whole planet makes in-atmo ships kinda more trouble than their worth. But there are plenty short range vessels that aren't ftl capable. Impulse in tng can get you pretty close to warp 1 anyway. When they're Starship they're called that because they are capable of interstellar flight. Thst being said, Quark also makes a big deal about getting his own warp capable ship in Little Green Men.
At this point I feel like the best way to get a ship is to become plot relevant and hope it's a lighthearted one off where you fly away sage at the end.
That is such a fucking gamble
Stsrfleet is Q's way of testing random weirdos with spaceships when they venture too far.