A Missouri Corn Cob would be the most affordable, but IDK I don't care for cobs much. Some do but I like briar and meer- it is just me. Personally I buy my pipes from antique stores, we call them Estate Pipes. Cleaning them up and making them look new(ish) is easy and very rewarding. I rarely pay over 10 bucks for a pipe and I have several Dunhill, Comoy, BBB, ect that would cost $400+ to purchase from a retailer. It takes me on the average about 2-3 hours to make a heavily crusted up pipe look nearly brand new. There are many forums/videos that explain in detail about this.
Pipe Magazine Pipe Smoking Forum it one of my favorite as well as
The Ivory Smoke Lounge over on Reddit.
With that said what brand would I recommend? Most any, but some come with some peculiarities that you may want to brush up on. Drugstore pipe come to mind here and I am speaking about Dr. Grabow, KBB, Yelo-bole, these are mass produced and normally have screw together fittings with little metal hooks/scoops/balls inside the pipe called stingers. They were used for various marketing purposes and gimmicky. Most were entirely machine made, some partially and the rusticated versions IMHO look terrible. However the briar used on these pipes, certainly the older KBBs are top notch. Regardless they most always are good smokers. The Best news is they can be had for $5!
As one may know pipes have been around forever so knowing a little about the brand helps when trying to ascertain if you have an expensive pipe or one that has a rich history like the KBB Brand. There are many collectors of all makes so the information is at times overwhelming, other times little is known. The large companies sold pipes as off-brands or seconds while some companies have been bought and sold and have moved to several different companies and back again it makes it hard to date your pipe. Here is some good reading to help identify the markings on pipes you may come across
Pipephil-Pipe Maker identification
The biggest thing is you need to find the pipes that speaks to
YOU. I tend to go for a billiard which is like Bing Crosby's pipes., I have some bents that are very comfortable to clench so it varies. Once you find the pipe that has caught your eye look it over for damage. Large chips, dents, broken bits, cracked bowls, cracks period-skip. Normally when I go hunting I take a flashlight, magnifying glass, and sometimes pipe cleaners, or even a strand of heavy string trimmer line. The first two are self-explanatory, the trimmer line is to check to see if you can easily pass the pipe cleaner through the stem. Failing to do so would indicate blockage or poor construction (or possibly a stinger). When trying to identify the makers marks I use grease from my nose as it highlights to roll stamp and gives indication of the grain better.
I love to find a giant basket of pipes with a sign that says $8.00 as I always find some gems. When finding the basket I approach it and I look for is drugstore pipes, if I like it I'll set it aside in a pile. After a while you can spot them quickly they usually will have a dull metal washer between the bit and stem. Then I'll look for the branding and segregate them too. Then ones that are unnamed (and many may be) I'll look to where they were made, England, France, Italy are the big three all fine pipes normally.
I gravitate toward European made pipes mostly English and French, however I wouldn't discount an Italian made pipe. Generally if it hallmarked it would be a higher end pipe but again not always. During some points in time the KBB Pipe company sold pipes that surpassed Dunhill pipes in cost by a wide margin. Pipes with Silver bands are generally higher end pipes but also may be repaired as they use silver bands to strengthen a broken/cracked shaft. Most have hallmarks too.
When are you looking at these you will find some are oxidized, dirty, caked up, ect. All easy to get past. If you find one that has so much build-up that it makes you wonder how it could be smoked that is a good clue it was a good smoker. Some old-timer used the shit out of it for reason. Here is a decent video for Clean-up of an Estate pipe.
He uses a reamer but you can use a knife to cut the cake just make sure you are not digging into the briar I've use children's safety sissors. Heavily caked pipes like his can be soaked in alcohol to loosen the cake.
Making a stem like new requires a trip the auto parts store for some 800/1k/ 2k wet dry sandpaper, micor fiber polishing pad can be had @ Hobby Lobby up to 32k. Polishing compound or carnauba wax.
I soak them in hot water w/Oxiclean and Borax then get to the sanding/polishing after an hour or two, normally I do this right at the start so by the time I am done with the briar it is ready to clean.
The above video maker has 2 more explaining the further detailing of his 2 pipes worth watching.
Or conversely if you find a pipe that you want to send off for a professional cleaning there are those who do this for 30-40 bucks and do a fine job.
Feel free to ask if you have questions. Tobacco choice is another topic of discussion all together. Lots of reading and experimenting to be had there.