Suggestion:
Quality requirements for the water will influence the construction.
Screw-bolted (demountable) metal frame constructions, inside (cheapest/corrugated/partly overlapping) mounted bolted metal or glass fiber screwed demontable plates, covered and inside sealed by flexible plastic sheet (adapted to tank form) All to be easily transported and erected at site. For potable water: Roof construction:tent formed fabric, reflecting 'silver' to cool, to hinder insects and animals, debris, to drain rainwater and withstand storms. All fenced in and/or protected. Maintenance, water tests and chemical treatment, and tank cleaning procedures.
Comment: Massiv constructed tanks are commercial more available and cheaper for somewhat smaller tanks than 1000 and 2000 gallons, and more easy to transport. Hence the idea of checking cost for lesser tanks in series. Perhaps also some mounted on top of each other? Several tanks in series will make it quite more simple to inspect and clean without shutting down the whole system.
Good luck!