When renting a cheap rental car, make sure to inquire about any special weekend or weekly rates. If your plans are flexible, you may be able to save some money if you rent during a price break period. Also ask about possible blackout dates when the advertised price you may have seen is not offered.
A deposit or "refundable charge" may be required upon arrival. This will be refunded once the rental vehicle is returned safely. It is customary for the rental company to charge this to your credit card, but not process it unless there is a contract breach. For some companies, it may be possible to leave a cash deposit.