Looking for kit around ~$850 with about a 300mm bed

Alright, so to begin, I've been working with 3D printers for a while now, and I was asked to build 3 kits for a commission. I currently own a TAZ 4, and it is my baby, but I've been promised one of the 3 printers if I build the other 2 for my client. I am looking for a wider printbed (hopefully more than 200mm). Now I've never used a delta before, so I am obviously more familiar with Cartesian printers. I would like to build a hardware kit from scratch, as it saves money and it would be great experience for me, but this is by no means a requirement.

Thanks for the advice in advance!

An additional note: I live in the US ATM.

Is 300mm printable diameter sufficient, or do you need 300mm square? There are several 300mm diameter delta designs around, including my Kossel adaptation described here [miscsolutions.wordpress.com] and the following two blog posts.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Going to say a square base is a must, since almost all my designs are rectangular in nature for the most part. I've been looking at the Prusa i3 12" or the Wilson TS, despite the 230mm size. The wood frame of the Prusa is rather off-putting, but the price is definitely good, however, I'm not on much of a budget here.

Some creative part sourcing should allow quality machine construction with that sort of budget. Take a look at my machine (linked in my sig, below) to see what can be done with scrapped machine parts picked up via ebay, from local scrap yards, and the local makerspace.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]