News that Avis Budget Group plans to buy car sharing network Zipcar for $500 million opened some eyes this morning. But this could have trouble going through, with a law firm announcing it is investigating whether Zipcar didn’t get the best deal possible.

Former SEC attorney Willie Briscoe and the securities litigation firm Powers Taylor will investigate whether Zipcar’s shareholders won’t get enough cash in the transaction.

Avis said it will pay $12.25 per share for Zipcar, a premium of about 50 percent over Zipcar’s share price on Dec. 31. But the investigating party says the Zipcar board may not have obtained the highest price it could have.

“Due to the proposed sale price, the size of the deal and other factors, we believe this transaction may undervalue Zipcar’s stock,” Briscoe said in a statement. “Our proposed lawsuit will seek to obtain the highest share price for all shareholders.”

Briscoe and Powers Taylor pointed out that one Yahoo Finance analyst estimated Zipcar’s shares to be worth up to $13 apiece. It’s also notable that Zipcar’s 52-week high on the stock market was $16.25 per share.

Avis said it expected the Zipcar deal to close in the second quarter of 2013, so we will see what happens.

Car crash image via Lee O’Dell / Shutterstock.com

RelayRides takes advantage of the wasted hours in the day when your car isn’t being driven. With RelayRides, car owners can make their car available for short-term rental, and approve the people who make rental requests. RelayRides takes 15 percent of the transaction cost.

The company received a $5.1 round of funding in March, which involved Howard Hartenbaum of August Capital and Joe Kraus of Google Ventures, both of whom are involved in this round.

When prompted for comment, RelayRides declined to provide details.

Since RelayRide’s last round of funding, its direct competitor Getaround won a Tech Crunch Disrupt award. Getaround performs the same service at RelayRides, while also engaging drivers through a mobile app, similar to popular car sharing service Zipcar. How RelayRides intends to compete remains to be seen, but already it has one edge: Car owners on RelayRides take 65 percent of the total rental fee while Getaround users get only 60 percent.

The virtual car rental space isn’t an empty one, and it is starting to see some niche offerings. For example, HiGear connects luxury car owners to customers looking for a cherry rental. The company covers insurance, verifies renter’s identity and does a DMV background check in order to keep transactions copacetic.

RelayRides was founded in 2008. The company is headquartered in San Francisco, Calif. and has a satellite office in Boston, Mass.

Getaround first started generating buzz late last year, but with its official launch the company has seemingly responded to every criticism it initially faced. It’s launching an iPhone app that will let you easily locate, rent, and open cars in its marketplace — which communicates with an even more impressive car-kit, that’s easy enough for anyone to install.

Most importantly, the company has partnered Berkshire Hathaway to provide insurance while your car is being rented. Berkshire provides full collision, comprehensive and liability coverage for every car in Getaround’s marketplace.

The company said that it structured everything so that there’s no risk to the owner. Getaround’s insurance doesn’t affect your current car insurance at all, and it only kicks in when the car is being rented.

“There are over 250 million personal vehicles in the U.S and they sit idle an average of 22 hours each day,” Getaround co-founder Sam Zaid said. That means there’s huge potential for the company to take off if it can assure users it’s trustworthy.

The service works much like Zipcar, except the owner is in charge of the availability of their car.  Renters can see when particular cars are available, and submit a request to rent it via the web or mobile app. Once the owner approves it, the renter can easily open the car using their iPhone (and I assume other phones in the future).

Getaround takes a 40 percent commission from rental proceeds — but 60 percent certainly isn’t a bad return when your car could be alternatively sitting in the driveway doing nothing.

The service also has plenty of advantages over the competition. Rental prices, which are set by the car owners, are generally cheaper than Zipcar or traditional car rental companies. Getaround also doesn’t have the problem with expanding like Zipcar does, since it doesn’t have to worry about deploying and maintaining a fleet of cars. It’s also just as useful in less densely populated areas as it is in cities.

RelayRides, another car-sharing startup in Boston, offers a very similar service, but at this point it seems like Getaround is pushing to build a more social marketplace.

San Francisco-based Getaround was founded in 2009 and so far has raised $1.5 million in funding.

Full disclosure: I own some Zipcar stock.