There are undoubtedly a slew of outlets where a person can buy a kit, but the connotation of a kit can sometimes belie the quality of wood and the skills needed to build a playable instrument. I've seen acoustic kits for less than $300 but I haven't seen one in that range that I would want to build - much less play.
A good kit, one that will use high quality materials and solid woods as opposed to laminates, one that will last a lifetime are available from four places that I know and recommend:
1 - Martin Guitars : https://www.martinguitar.com/1833-shop/#!/c91/s94
A dreadnought kit sells today for between $500 and $550 depending upon whether you want to build with Mahogany or Rosewood back-n-sides. Some of the materials are preshaped: sides are pre-bent to shape, the dovetail neck is formed, the fretboard is slotted for frets, the top halves are joined with the rosette installed, braces are rough shaped, and bridges are slotted for the saddle. The booklet that comes with these kits is almost worthless unless you've already built a number of guitars and in that scenario you wouldn't need a booklet. Martin frequently puts their kits on a 25% sale pricing so a good quality kit is highly affordable.
The kits themselves are great to work with and can produce a guitar that will sell for between $1500 and $2400. I've built a number of them and love the tonal qualities and in most instances I have built from the base kit and customized the guitar by adding real ebony fretboards and bridges, upgraded tuners, upgraded binding, back center strips, and inlay. The most recent two that I built also included installed LR Baggs Lyric Anthem pickups and the total cost of materials came in around $1,000.
The following are a couple of links where you can judge the sound quality of a Martin kit for yourself:
Check out more videos and a video of the build process at www.scismdesigns.com/guitars-ukes
Photo: Martin Kits unboxed
2 - Blues Creek: http://bluescreekguitars.com/product-category/blues-creek-guitar-kits/
Blues Creek is an authorized Martin repair facility, the owner worked building Martin guitars for a good number of years and his kits are pretty consistent with the Martin kits themselves. Blues Creek is a great place to pick up parts and some tools needed to build. Kits prices are around $675. Again, nice quality kits and the owner is a heck of a nice guy and responsive if/when you have questions
StewMac is a go-to site for a lot of folks that need tools and materials for instrument building, and while their tools can be on the pricey side, their kits are competitively priced to the Martin kits. StewMac also offers kits with very high quality woods and some of these kits will run in the neighborhood of $1,200 or so.
Like the other two retailers mentioned above, StewMac kits come with similar pre-shaping of parts. StewMac offers both dovetail and bolt-on necks and they have an entire array of parts that you can purchase to upgrade your build. Their instruction booklet is much more detailed and informative than that provided by Martin Guitars but if this is your first build there can still be a bit of a gap in covering some details of the build.
4 - Luthier Mercantile International: https://www.lmii.com/
Luthier Mercantile International (LMI) provides a great deal more customization in their kits than any of the other three and the site uses an easy to follow "wizard" to step you through selecting which types of wood, tuners, binding, etc. for the build. Selections of "AAA" grade wood for the tops is possible from LMI and is a part of their wizard's build process. One of the more impressive things about LMI is that you get to actually see which woods and bindings you are thinking of purchasing. You don't simply select a wood type, such as an Engleman Spruce top, for example - but, rather, you get to select among the several such wood types and actually see and choose from the available sets. Their kits don't include any pre-shaping of parts or materials and this may be daunting for a first-time builder. That said, in their wizard they do provide options to have elements pre-shaped or pre-built. For example, they will bend and thickness the back and sides, they will rough size and slot the fingerboard, they will provide a pre-shaped and slotted bridge. These modifications not included in the standard kit pricing but they are amazingly affordable. A kit with some customization and pre-shaping will run around $750-$800. But you're getting better wood qualities and selections. Their staff is tremendously helpful if you have any questions.
I hope you find this information useful. Please check out my site at www.scismdesigns.com and keep your eyes open for future editions of this blog which i send out roughly every other or every third week. I will soon being offering blog posts covering the actual build process, addressing techniques, tools and jigs as well. If you have any questions, please feel free to write. My book will be available in the near future, excerpts will be available through this blog and a spiral bound copy will be available here and in digital copy as well.