Series pumps. Not a great idea. It gets expensive, after a month or 2.
Gas, generator maintainence, time, etc. I'll say its better to bite the bullet now.
Get a good pump that will do it for a long time.
I would suggest looking into 12V battery pumps, 12V panel(s), 12V battery, tank / pump controller, etc.
Then set the LVD a little high (12.2V). Let it do what it can, when it can.
Not sure $300 will buy the panel.
Still a cheaper option,
G-