You may want to look into "modifying" a "salvaged" screw conveyor if you're looking to minimize the cost.
Do an Internet search for "Archimedes Screw Pump," and you will find a number of references for kits, etc.
The only industrial ones that I have seen are quite large, but I've never been serious in looking to apply one anywhere. Since you are wanting to pump from a ditch, I presume that you will be needing something that is very "trash tolerant." This is not an application where efficiency will reign supreme.
Solar?? Are you sure that a small solar PV array will be adequate? Is this for just intermittent use with a relatively large battery? My guess is that pump efficiency will be an issue for solar. If this is a remote site, what about using wind (something similar to the old windmills that were common on US farms 50+ years ago)?
Because of likely trash issues, you may want to consider a larger pump running intermittently just for its ability to handle larger trash items.
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.