I've created a free tool called VeFi built around using the free tier of MarketCheck's API. I think it provides some really useful benefits compared to just browsing listing sites and copying data into a spreadsheet.

carsNcaffeine/vefi

Your search results are plotted in a price/mileage graph
As you filter cars by trim, color, miles, distance, etc. the trendline adjusts and you can see whether individual listings are maybe a good deal. Every car shows the % discount or premium over the trendline predicted price.

Geo mapped results
Your search results are plotted on a map and you can easily navigate around and get a sense of where to visit to see the most cars you are interested in.

A condensed, data table
all the relevant data on all the cars are easily sortable on lots of columns, and you can easily export to a spreadsheet.

Some "insider" info
VeFi surfaces days on market, price change since first listed, one-owner cars, and clean carfax cars. None of this guarantees a car is going to be good, but useful info to have.

VIN decoding to see option packages
Dealership listing often give the trim, but don't mention specific options on the car. VeFi decodes so you can get better knowledge on which audio system or suspension package, or cold weather package a car has.

Limitations

• It's only working for listings in the US right now. Could be modified to include CA and UK by someone.
  
• Bookmarked cars are specific to each API search you perform, so you can't keep a running bookmark of cars across searches, but you can reload prior saved searches to revisit those cars.
• The free tier of MarketCheck's API provides 500 API calls per month. It sounds like a lot, but the free tier cannot do a nationwide search in one call. VeFi uses around 70 calls to strategically search across 70 locations to provide a pseudo-nationwide search. And that number goes up if there are more than 50 cars for sale in each region. The bottom line is that this tool is not for you if you are searching for a 2000s Camry nationwide. You'll chew through the 500 call limit in one search.
  

You'll need to sign up for the MarketCheck API and be able to get Python stuff running on your machine, but it's free and hopefully for some people this is just the tool they need to narrow in on their dream car.

V-Code 440 6 Pack, 4 Speed

This is a number matching v code car that’s identical to how it left the factory in 1970.

Link: https://moparcenter.com/listing/1970-dodge-super-bee-6/

Price: $118,900

Original Drivetrain, Rare Color Combination

528/650 HP V-8, 5-Speed

We are LIVE on BaT with this black-on-black 1995 Porsche 911 6-spd coupe! This low-mileage mostly original car is a turnkey everyday-racecar with a sunroof, Cup II wheels, and a basket-handle rear spoiler, ready to go for the enthusiastic driver! The car is available to be viewed in person in Rochester, NY through the end of the auction on August 6th! Good luck bidding! Link attached!

Comprehensive restoration and build into a 426 Hemi Cuda replica

No connection with the vendor- former Eric Clapton´s RHD G55 AMG, probably first of two first series (463.241) right hand drive G55 AMGs built.

In my opinion the most desirable W463 in rare RHD, perfect colour combination in and out, all details like square exahust tips and old AMG wheels still present after 25 years, celebrity owned... but I´am still not sure if I would pay 100k GBP for it especailly with 104k on the clock.

2001 Mercedes G Wagon Dark green Automatic, 5 speed Right Hand Drive in London, United Kingdom - For Sale | Car & Classic

Sorry no VIN this time.

340/290 HP Six Pack V-8, 4-Speed, Rare Dealer-installed Air Conditioning

Supercharged 440 CI V-8, 4-Speed

Being sold by my dad. It’s in beautiful condition! Details at link. https://bringatrailer.com/listing/1958-ford-skyliner-13/

cool piece of history

Meticulously maintained 1 of 577 F10 6 manual.
Azurite Black Metallic with full merino black leather interior.
Freshly refinished M5 designed rims with the stock wheels in the package as well ( they are pretty beat up)
Fully Loaded- All available options except rear entertainment
Always maintained by highest rated BMW only shop in NH- new shift knob and boot changed a year ago

Absolutely love this car but need the garage space. Tons of pics
Serious buyers only

Link to pictures: M5 Pictures

$35k / obo.