My Lowes store has tongue and groove paneling sheets in the store but I don't see it on the website.  If I get a chance I will stop in and get information.  It wasn't that expensive and looked nice. 

Measure the square footage of the interior you want to finish. Add 20%. Divide that figure by 14 and that will give you the number of packages you will need. Multiply that by $14 and you will have your cost for the paneling part.

Gard

I bought the unfinished tongue and groove look wood paneling - purchased it at Home Depot - and just finished it with two coats of varathane varnish.  We used pine tongue and groove planks for the cabinets with the same finish.  It came out really nice.  I keep meaning to post some pictures of the finished project. 

It's a 3 1/2 foot short wall.  It has two lower cabinets, two overhead cabinets and a utility closet.  It's not very big, but it's fine for me and a close friend!

Lumber is sold by the Board Foot.    1 foot x 1 foot x 1" thick.

Any lumber you pick up is ultimately priced using this formula.  A 4" wide by 3' foot long by 1" thick piece still = 1 board foot.

Suppliers that sell wood flooring will also be an option. Wood flooring comes in 2-3-4-5-6" wide planks in almost ANY hardwood you could desire. You can buy it already distressed, hand scraped, pre finished or raw and you will need to finish it.  Most wood flooring comes in 3/4" thick pieces in the unfinished woods.  3/4" finished = 1" rough.  So even though you get a 3/4" piece, it started as a 1" thick and was planned on 4 sides to give a smooth surface. The result is that it's now 3/4" and you pay for 1"

They also sell Engineered Woods.  Where they place a thin veneer of real wood on the surface and add a backer of a manufactured wood.  Something like a particle board or MDF material.  These usually sell for less than a real plank of wood, mainly because you only used 1/8" thickness of real wood. The arguement for them is that they are more stable. Less prone to swelling and movement due to moisture in a home. They also come prefinished. The ceramic coating they put on in a controlled oven is hard to match with an on-site finish. And hey usualy are ony 3/8" thick.  Because they are thinner and use a filler material for backing they usualy weigh a lot less than real wood.

I usually figure that real hard wood. Oak, Maple, Ash, Hickory, will run about $2.50 to $4.50 per sq foot in random lengths. I much prefer the real wood vs the engineered wood for a home floor. It just wears better and if damaged I can come back and resand it and refinish it. An engineered wood can not be resanded since the finish is very very thin.

Any of these flooring products wil work for wal paneling. They are have some kind of a tongue and groove . The engineered products have a snap/click edge that holds them in place.

 4x8 paneling is another option. And most people think of for walls in homes.  Since it saves so much time in labor. These sheets are usualy only a 1/4" to 3/8" thick.  They will bow/bend  somewhat. And while the stores may not stock a lot of variety. The manufactures do make a broad spectrum of woods and color choices. Go into a lumber yard and ask to see their panelling catolog and have them order in what you want.  Of course if Lowes or Home Depot stocks it, it will be cheaper.

We have a company nearby, "Builder's Surplus" that sells flooring at greatly reduced prices. They buy the end runs and sell finished flooring for as little as $1 sq/ft. You have to make sure you buy all you need up front. If you need extra materials later, there is a poor chance of getting a matching product.

As PH stated, the factory applied finishes are durable and evenly applied. It is almost impossible to duplicate them in the field.

Gard

Something I've noticed is the T&G @ Home Depot & the T&G @ Lowe's is different.

The stuff I've been getting at Lowe's isn't very sturdy or thick (compared to other materials I could have chosen) & I don't think the weight is extremely different, depending on what other option you would have chosen.