I'm in the (slow) process of building out a kitchen in the back of an e350 RB. I'll try to post a couple pictures, but I have to get them onto my website to insert them into my post, so it will take a day... I have a full woodshop and have built out cabinets and drawers in the past. However, I am far from a competent woodworker...
If you are building it yourself (you'll need a buddy with a table saw, router and an extra pair of hands). I think the wood materials with drawer slides and assorted hardware would set you back in the ballpark $500. A quick build (think experienced buddy) is probably a long weekend of effort. A more intricate build would be a couple weekends with time in-between for gluing, sanding, finishing, etc. Add at least $50 in beer budget to thank your buddy for covering his shop in sawdust.
I won't get into costs on utensils, plates, etc. But the big items are a stove ($100) and fridge ($500 - $800+) and sink ($50 - $?,??? +). . The gotchas (time and money-wise) that aren't included are electric and plumbing. You can easily spend a Franklin and a weekend just wiring a 12v fridge. But, you probably need a house battery and maybe solar to really make it go. Hard plumbed propane is the same way. The sink can be a craigslist bar sink with hand pump connected to a couple jerry cans to a full tank and graywater setup.
If you want to buy more of a turnkey setup I think you'll spend a couple grand on the case and slides. You can probably bolt it in after work some evening and will probably spend 10x as long picking the right one and waiting for it to get delivered. I love
Drifta's designs
https://www.goose-gear.com/collections/campkitchen also seems to have some great stuff. I'm guessing a local van upfitter could probably hook you up without having to do any work.
I'm betting someone else here can recommend a shop in California that does that work or other manufacturers that have cool kitchens for Econolines.
FWIW: we still use a
cooler, a jerry can, two dishtubs and a really well worn coleman stove and a
folding table. The advantage is that we can cook out the back of the van or move camp away from the van depending on our needs. We often try to basecamp somewhere for 2 or 3 nights and then setup away from the van under a pop-up. We're into this setup about $500 so far. It took us two long trips (a couple weeks each) to dial it in, but we love it now! I can cook for 3 - 8. When traveling solo, I'm setup or packed down in 5 minutes in the back or side of the van depending on sun and wind.