Collecting Vintage Race / Grand Prix Posters has taken off just like most other collectibles.
There are marque specific factory posters (eg, Porsche, Shelby) as well as famous races like Le Mans, Sebring, and Monaco GP that bring big money (eg, $1000+).
If you want to build a collection or just fill a wall on a garage or man-cave then ebay is your best bet as you can pick up original vintage posters for <$25 and cut/matt yourself on store metal frames or professionally frame for $50-75 and slowly build a nice collection around you car, geographic locale or favorite foreign track/travels.
If you want to target specific genres like the 1960s Grand Prix era or specific artists (eg, Zito, M. Turner) then your investment will easily reach into the $1000 to $5000 range as you find investment grade pieces, famous artists and famed marques (Bugatti, Ferrari, etc) and build a collection of 20+.
Ebay is still best for originals for usually $10-100; most are 18" x 27" and framed can look really great. The more famous ones will be $100-150 (eg, 60s Monaco GPs). Large 20"x30+" pop-art/colorful ones from 1960s with iconic cars like GT40, 917, Chapparal, P3/4, Lola, Can Am can easily reach $250+. Large format bold colors posters of 30+"x 40+" are the rarest and were usually from track entrances, billboards, stages, auto shows, showrooms or VIP/PR events, and bring $500+.
I you want to just click/buy there is a huge range of vendors below that have everything from $20 retro-inspired modern race poster, to hi-res digitally shot prints on canvas, to art galleries selling $500-1000+ pieces.
Super rare originals of all of above can still be found for $<50 if you really search on EBay's UK, French, Italian and German sites and/or have key words/dates of specific/exact posters. That's what makes the hunt the most fun!
VENDOR LIST:
As with all art, I would highly recommend avoiding the reproduction art/poster websites that list the generic Monaco, LeMans, etc race posters.
The quality of the prints is low/pixleated, the frames are cheap, stapled together, and backing is not archival. You can easily purchase authentic, vintage pieces on eBay for less all-in cost.
Original Vintage Vendors:
http://www.vintageautoposters.com/
http://www.car-poster-gallery.com/cat_27_126/original_race_posters.html
http://www.historiccarart.net/acatalog/Original_Race_Posters.html
http://www.arteauto.com/lemanspostersmonacograndprixpostersvintagepostersandrazziaposters.aspx
http://www.posterclassics.com/vintage-auto-posters.html
http://www.motorsportcollector.com/cart/index.php?main_page=index&cPath=5_75
http://www.collectorstudio.com/index.cfm/ID/10/itemTypeID/31?pagenum=2&itemTypeID=31
http://www.24heuresdumans.co.uk/content.php/000
http://www.juliasantengallery.com/index.php?b=gallery&subcategory=Auto Racing&Page=2&Paging=Y
http://boutique.lemans.org/catalogue/all/all/affiches.htm
http://www.locomobilia.com/from-1945-to-1970_c_359.html
Sources of Retro inspired: Posters, Digital & Canvas
http://www.camilopardo.com/shop/
http://www.trilon.com/bapom/posters-largeformat.htm
https://www.pullmaneditions.com/items.php?collection=10
http://www.nicolashunziker.com/
http://www.grandprixposters.com/grandprix-posters/european-motor-racing.html
Raceshops of: Watkins Glen, Road America, Pitt GP, Ford Archives; and Misc.vendors.
http://www.pelicanparts.com/catalog/ShopCart/STUF/POR_STUF_POSTAB-detail.htm
http://www.grandprixfestival.com/Posters.html
http://www.roadamerica.com/store/collectibles.html
http://lime-rock-park-merchandise.myshopify.com/collections/prints-posters
http://www.scottadvspec.com/stores/pvgp/PostersLithos.htm
http://www.autotrend.com/atg/mercha...=30&SortBy=id-desc&Category_Code=Dennis_Simon
http://www.tomsimport.com/new/parts/parts.asp?sect=57&new=1
http://www.timlayzell.com/motor_art_prints.htm
http://products.theconcoursstore.com/index.php/posters.html
http://fordimages.com/perl/collecti...082&pgNumber=1&seeAllImages=1&itemsPerPage=-1
http://www.steveaustinsautomobilia.com/index.html
http://www.circuit-des-remparts.com/notre-boutique-54,lithographies-50x70cm-11.html
Ebay key word searches: major races, tracks and venues are the most collectible
Le Mans
Monaco GP
Sebring
Brands Hatch
Mallory Park
Goodwood
Silverstone
Snetterton
Spa
Brno
Mugello
Monza
Indy 500
Reims
Rouen
Pau
Albi
Watkins Glen
Can Am Series
Riverside
Sears Point
Laguna Seca
Monterey GP
Mid Ohio
Lime Rock
Daytona
Interlagos
Imola
Mille Miglia
Carrera Panamericana
Pebble Beach
Meadow Brook
Rex Mays
Mosport
Nurburgring
Hockenheim
Vintage Race Clubs:
SCCA
USAC
ARCF
BARC
ADAC
AVUS
Famous artists are
Geo. Hamm
Beligond
Zito
Michael Turner
Dexter Brown
Nic Huziker
Enjoy and build your collection selectively and slowly!