I have made a router table from some plywood and 2 feet of 2 by 4. The first step is to take the plastic plate off of the bottom of your router. If your router doesn't have one, tough luck. i traced the plate centering the hole for the bit to go through the best i could. i made the hole bigger because my 45 degree edge bit didn't fit through the original hole. I cut a starter hole and then got the jigsaw and finished cutting it out. make sure when tracing the plate to make the screw pattern so the depth locking mechanism is in front of you when you trace it. I got some machine screws, the ones that fit were 24 thread count, and make sure they are long enough to g through your plywood and to thread into the router base. Drill the holes you traced then countersink. If you don't need a fence you are done. I needed a fence. I put an oval hole 4.5 inches from each left and right edge, 2 inches from the far edge of the table and rough on a line i struck across the whole table ,through the middle of the bit hole. 2 inches from the far edge, and 4.5 inches i drilled a hole the 4.5 inches from the edge and parallel from the bit hole, the cut on a line on the tangents of the 2 holes just drilled. you now have an oval hole. mirror it on the other side. i cut a 2 by 4 at the width of the table and then put holes 4.5 inches from the edges of them and drilled holes there. put a bolt through the oval and the hole in the 2 by 4 on both sides. theres a fence. I spent approx. $15 0n the wood and screws/bolts so low cost too.
You will need a jigsaw and a circular saw
Dress your boards. Cut the pylwood to your desired size, i did 2' by 2' 2". Cut your 2 by 4 to the dimension of the long side of your table.
Trace the plate of your router on the center of your board. Drill a starter hole in the bit hole to put your jigsaw blade in, then cut it out. drill the screw holes to the diameter of the machine screws you bought. countersink your holes, but not too much. I used a 0.5 inch countersinking bit.
Drill a hole 4.5 inches from the left edge of the table and 2 inches from the far edge. Drill another hole 4.5 inches from the left edge and directly on the left of the bit hole, in line with the first hole. cut a line with the jigsaw on the connected tangents of the holeson each side, you should have an oval hole. Mirror on the left side. The picture is rotated, the top on the picture is on the left of the router table.
Drill a hole 4.5 inches from the left edge of your 2 by 4 and in the middle of it. Mirror on the other side. The picture has the 2 by 4 with the bolt
Remove the bottom plate on your router then line up the holes and screw in the router.
Put bolts through the holes in the 2 by 4 and then those bolts through the oval holes , thus obscuring part of each hole. put a washer then nut on each bolt which should be through the bottom.