Electric-vehicle startup Rivian Automotive Inc. is discontinuing the cheapest versions of its pickup truck and SUV models, citing low customer demand.

Eliminating the base version, dubbed the Explore package, now means the most affordable pickup truck in the R1T model line will have a price of $73,000—an increase of $5,500, Rivian said in a post on its website. The least expensive version of its all-electric SUV, the R1S, is now $78,000.

“We realize this news comes as a surprise and apologize to customers who have had their planning impacted,” the company said. Rivian said it notified customers Thursday.

Rivian Chief Executive RJ Scaringe has sought to simplify the array of options the company initially offered for its vehicles to increase production numbers. A Rivian executive, speaking on a podcast, said discontinuing the low-price packaging options would allow it to manufacture more vehicles quickly.

This is the second time that Rivian has adjusted prices for its vehicles as it confronts rising raw-material costs, particularly for batteries, and manufacturing difficulties that have led the company to report a $1.7 billion loss for the second quarter.

In March, the company increased prices for its vehicles by as much as $20,000 for some customers, including those who had already put down a $1,000 deposit to reserve their vehicles. Mr. Scaringe two days later issued an apology following customer complaints, saying Rivian was wrong to apply the price increase to those who had already reserved a vehicle.

Rivian shares were down about 5% in morning trading Friday following the news of the changes to its vehicle pricing.

The California-based auto manufacturer is slashing costs to conserve cash and giving priority to certain trims of its vehicles in an effort to boost factory output. Rivian said it aims to produce 25,000 vehicles this year from its plant in Normal, Ill.

Rivian isn’t the only EV company raising prices as a result of rising materials and production costs. Tesla Inc. and Lucid Group Inc., two rival electric-vehicle makers, have raised prices this year. The average transaction price for an EV in the U.S. was over $66,000 in July, around $20,000 more than the average gasoline-powered vehicle, according to car-shopping website Kelley Blue Book.

The higher price point presents a particular challenge for Rivian with lawmakers proposing changes to a federal tax credit for EV buyers that would set a cap for qualifying models. Any electric truck or SUV selling for over $80,000 would become ineligible for the $7,500 tax credit under the planned revisions. Rivian has said that most of its vehicles would no longer qualify as a result.

Parts shortages and supply-chain issues are hammering the entire car industry and falling hard on young auto startups that are still trying to spool up their factories.

While many car makers, such as Ford Motor Co. and Toyota Motor Corp. , are enjoying healthy profits despite production struggles, newer companies like Rivian that produce few cars are still losing money.

This is a critical period for Rivian, which is in its first full year of building vehicles and under pressure to show investors it can transition from a promising startup to full-fledged auto maker.

The car company has had to overcome a slow start to the year where its assembly lines were running well below capacity, mostly due to difficulties getting semiconductors.

The line rate has improved since then, and Mr. Scaringe said he expects to have the production lines running at full speed by the month’s end.

Still, it is burning through cash. At the end of June, it had about $15.46 billion in cash and cash equivalents, about $1.5 billion less than at the close of the first quarter.

Write to Sean McLain at sean.mclain@wsj.com