Yes, you are looking at roughly 1800 gallons. Suggustion, you will want a 1 foot marginal plant shelf around the edge of the pond. If you are stocking it with Koi, the pond really needs to be 4 ft. deep. If you are not stocking it with Koi, then a 2 foot depth is easier to maintain and you will have better options for plants in the center.
You can easily make a "homemade" bio filter. We made one that sits at the top of our waterfall. The bio filter is 100 gallons and it services a 2500 gallon pond. We used a tub with filter media. We also have potted plants that sit in the bio filter atop the filter media. We flattened an old milk crate for them to sit on instead of buying the pricey pre made grates for bio filters. Make sure your pumps are located at the opposite end of the pond from where you position your waterfall and biofilter.
If your pond is in full sun, you will want plants covering 70% of your surface water space. This will help with algae control and provide the fish shelter from the sun.
As far as what this will cost, there are so many variables. The best advice I can give you is to calculate known costs like liner, pumps, hoses, etc. Figure in cost of plants, planting media, pots, etc. Figure cost of water conditioners and fish. Take all these costs and DOUBLE them...that will be your actual cost with a pond. It always takes more than you originally figure.
Good Luck and post some pictures.