Your location is going to make a difference for what kind of pump and capacity you need. In California, electricity is ridiculously expensive and it's worth it to invest a few hundred dollars in a quality, energy efficient pump. I have a 3000g+ pond and I DIY'ed the filter system. I took a large Rubbermaid tool box and put bulkhead fittings on each end. I sunk the tool box in the ground so water can gravity flow from the pond. There are a couple of pieces of pvc which hold bottle brush type pond filters. (do and Amazon search, loads of them available) Then, some Japanese filter mats. You can cut them, they are neutral density, and they're stiff. Matala (Amazon) mats are available in different coarseness. The water flows out to an inline pump. Many pond filters are constructed somewhat like this. Some put the box in the water. (you don't have to worry about waterproofing) Some put the pump in the water and gravity flow out of the box. Depending on your load you may be able to do a canister type filter with a 5g bucket. My first home made system was 3-55g drums linked together with media.
There's loads of stuff you can DIY if you're inclined. The Rubbermaid box is my 2nd mechanical filter. I flow from the pond into a vortex separator. Basically it's just a big cylinder with a conical bottom. The water enters the side, near the bottom, at an angle and drains off the top. This causes a whirlpool and the heavier sediment settles into the bottom of the cone where it can be drained off by a valve. Then it flows into the RM tool box. From there it's pumped into a 2ft wide 8ft long 3 ft high box with bio filter pads in the bottom and immersed plants on top.
Lots of folks make pond filters with storage boxes. I liked the tool box because it's really sturdy. It's about 1/4" thick and is made with the same stuff as the 300g stock tanks. Plus it has a hinged lid.