I would go to the box store and get 4 pieces of Birch plywood cut to 30" or 27" X 18" wide.... all the same. Then make a 1 X 2 frame around each panel to make it stiff and for support. Now you can arrange them in any order you wish. For supports use two saw horses with long 2" X 4" underneath in notches or get the work tables with the notches molded in... Stanley? Then you can attach them together using 1/4" bolts.
For the circular saw, drill 4 small 1/8" diameter holes in the base that are easy to get to. Line up the base edge so it's parallel to the frame you made. Screw it down with the blade in the center of the panel. Then turn the saw on and lower the blade through the panel so it's exposed on the other/top side.
For the router, locate the hole for the bit in the center of the panel and drill a hole from 1" to 1/1/2" in diameter for the largest bit you will use. Center and attach the router base using "Z" clamps or screws through the base.
For a fence, use a straight edge locking bar clamp that has a handle at one end with your push down and it tightens against the panel and frame. You can make a series of parallel lines on the panels using a drywall "T" square for reference when setting the fence OR use two stick down measuring tapes, one at the rear and one at the front. Now slide the bar clamp to what ever dimension you want at both ends and tighten it down.... no further measuring needed. More than one clamp will work, one for the saw, and one for the router.
Low budget and minimum labor to build, but very versatile, and can be disassembled easily for storage. I should have made one like this when I was starting out. Use a power strip switch rated at 15 AMPs to control each tool separately, one for each. Do not reach under the tables to turn them on and off, use a switch you can easily reach from above.