Car rental rates can expand and contract almost as regularly as the bellows of an accordion at a polka dance. One moment, they're cheap enough to rent an SUV for the weekend, the next moment they spike to the point where you have to scrimp and hope everyone will all fit into an economy car.

Admittedly, renting a car isn't essential for a getaway vacation, but it sure adds to the convenience element. Still, it's an extra box to tick off when you're planning your holiday and one that can be unpredictable when it comes to your wallet.

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Regarding those variances, folks in the rental car industry will tell you that rates are highly dependent on factors like state taxes, fuel prices, and insurance premiums, but those are marginal at best. For example, Michigan has the highest car insurance cost in the country, yet vehicle rental fees in places like Detroit are closer to the national average.

But remarkably, some rates are not only consistent over time but also downright cheap compared to what's offered elsewhere in the U.S. And if you stay as close to the beaten paths taken by other vacationers, you might save quite a bit.

Florida Keys (to a great car rental deal)!

If you're willing to bet on which city consistently tops the list of the cheapest car rental rates in the U.S., here's some advice: You can't go wrong picking a metropolis in the Sunshine State.

Almost every year, a Florida city will most likely occupy the top berth, usually Orlando, although the latest results from 2019 had Miami as the cheapest in the U.S. with the super-low daily rate of $23. Orlando finished second at $24, with Jacksonville in third at $25. Another Floridian destination, Tampa ($38), ranked eighth.

Las Vegas ($31) and Los Angeles ($32) rounded out the top five, while Dallas ($35) and San Diego ($36) ranked sixth and seventh respectively. The remaining top 10 consisted of New Orleans ($41) and Salt Lake City ($42).

Don't expect any breaks in Ohio

Ohio is best known as the Buckeye State for the chestnuts that grow in the region. But it might be equally applicable to how large your eyes shockingly expand when you see how many bucks go into renting a car in two of the state's bigger cities. The daily rates to get a vehicle in Cleveland sit at $84, the highest in the US. Rates in Cincinnati are hardly a bargain at $82, placing it second overall.

Offering minimal relief to your wallet are Newark, N.J. ($81), Anchorage ($80) and Boston ($74), ranked among the five most expensive car rental destinations in the country. As for the rest of the top 10, the damage to your travel budget is slightly less severe in places like Pittsburgh ($73), Seattle ($71), Portland, Ore. ($70), Denver ($69) and Indianapolis ($69).

It could be worse. Are you up to forking over nearly $1,200 US to rent a mid-size vehicle for a week in Phnom Penh, Cambodia, ranked as the world's most expensive city to get a car rental?

Location, location, location... and other rate secrets

Determining rates isn't rocket science, it's far worse. At least when you're building a spaceship, you have something called astrophysics on your side. Rental car rates depend a great deal on economics, which is far more unpredictable. But anyone with a rudimentary understanding of supply and demand would likely wonder why major tourist centers are so cheap since that's where much of the vacation traffic goes.

In those spots, anyone who buys a vacation package can get lower car rental rates from a company willing to mark down enough to be bundled into a one-stop-shop incentive that includes airfare and accommodations. That's especially the case in Orlando, where a lot of package deals entice visitors to flock to Walt Disney World.

Even if travelers opt against a package, there's more competition among companies for the car rental buck, so prices stay relatively low. In relatively more industrial cities that don't rely so heavily on a tourism revenue stream, proportionately more business-oriented folks are more likely to rent vehicles and are able to foot the higher bills.

The bottom line is, if a car rental company lot is full, watch for rates to drop. If it's nearly empty, be prepared to pay through the nose.

Here's how to get a cheaper car rental rate

Most of the time, varying car rental rates among destinations aren't likely to dissuade travelers from leaving home for the holidays. But if you're serious about saving money, shop around and take advantage of sites online offering all sorts of deals.

Also, pick a vehicle small enough to suit your needs. Larger vehicles like SUVs come with higher rates. And if you're risk-averse when it comes to your budget as opposed to the environment, be aware that more eco-friendly vehicles like hybrids and electric cars are also on the expensive side.

You'll also save plenty if you opt against buying additional insurance when booking a car. But make sure to first check with your credit card or insurance company to see if you're already covered when it comes to driving a rental.

The biggest saving you'll realize is if you avoid booking a vehicle at the airport. Taking a shuttle downtown to a car rental office instead could save you as much as 30 percent.

And finally, if you decide against a rental altogether, find out if your destination has a good public transit system or at least a few ride-sharing companies like Lyft and Uber operating in the area. At the very least, those options will result in additional savings.