Before 1990 CMC (FF too) sold a kit for around $8k plus shipping ($1k+) and you supplied the VW donor car. The kit included fiberglass seats, cut foam and sewn vinyl for the basic seat; gauges, wiring, emblems, nuts/bolts were extra; it had the vinyl top and frame. There are still unbuilt kits still in the box from CMC out there. Some appear as low as $6-8k but expect to in for 16-20k +.
You can buy a fiberglass body and sub frame or tub frame from places like KitMan. The other parts can be sourced as you get to them - be sure to add up what they will cost before you jump in on a new kit. You may not be completely happy with say a vinyl top in old CMC kit but you can upgrade later. Doing an update to a running built kit when purchased for reasonable $ is probably the cheapest was to get into the hobby - but over time the upgrades will add up quickly.
Here's couple currently on SAMBA for under $19k-