You can buy 3pc of 1/2" plywoods ($ 30); 30pc of 2x4s - 8' long ($ 80) 3pc of 2x8s - 10'long ($30) wood nails,screws and 10pc of blue concrete screws with a drill bit ($30); and 15'x20' EPDM45 liner($150) .Cut one plywood in half;build a frames using 2x4s for all 4pc of plywoods the same way you would build walls in the house ;screw all panels together- the inside dimension will be 96"x40" or 88"x48" and 4' tall.Secure the panels using blue screws to the concrete floor.Install liner.Make a picture frame using 2x8s,place on the top of pond and screw thru the liner to panels.Total cost is $ 320 and it is 735g when filled.This is what i am using as temporary pond to spawn my koi.It took me one day to build it and about 20 minutes to take it apart and store it in my shed.You can build it half the size - 2' high instead of 4'.Then you save about 40% of cost and it will give you little bit more than your 300g.- just another idea.