Sounds like you need to call around on a price on both.  Unless it is a large trailer, 30-k sounds high for a 5' shell trailer.  Around here 10 o 12' shell 3 horse trailers are right around that price. (4 Star, Bloomer, Elite, Platinum, only one I did not price was a Hart)

Depending on what you are wanting inside,  I just done our 2' short wall S&H steel trailer insualation, wood walls and ceiling and 2 lights for around 200. bucks.  But we did not want anything fancy just something to make it cooler in the summer and warmer in the winter to change.  Fixing to add a cabinet from Lowes in the nose and the cost is around 60. bucks for a complete setup, then  I will clear it or stain it like the walls. 

If you was around Texas there is a couple of companies that does small jobs like you are interested in.  Bunkhouse Conversions is one of them, check out their website it has prices and options listed.

If you screw two boards together and subject them to movement, the screw hole will elongate and loosen the joint. If you use a polyurethane construction adhesive, it will allow some give, even though the joint will be stronger than the wood itself. Using a pneumatic pin nailer on the tongue to hold the boards in place until the glue sets, would eliminate the sight of any fasteners. It is also a less expensive and time consuming construction process.

Pine and Cedar are similar in strengths, with the White Cedar being slightly lighter and having a softer face. Also if you work with NE white Cedar, the colour will be similar as well. The Red Cedar will vary in colour form a deep Mahogany to a white sap wood.

I purchased a large lot of Western Red Cedar a month and a half ago, and the board foot price was almost four times that of #2 White Pine. Pine can easily be stained any colour you choose, so the value for the additional cost for White Cedar is questionable.

Any of the three woods would make a very attractive interior, and are easily worked with common wood working tools.

BOL  Gard

Most furring strips are a little less than 3/4" thick; adding to it the width of the tongue, and its off set of the finished materials, you should be able to use a nail of a 1 1/4" length.

The urethane adhesive is strong enough to hold the goose flooring in place without mechanical fasteners. If you do use screws, do not use any steel or especially galvanized products into the aluminum. Stainless is the best.

If you plan on a finish for wood surface, do coat the backside as well. Spraying is an excellent process, and the individual cuts can be touched up with a brush later. The reason for coating all of the surfaces, is the absorption of moisture. If only the front surface is coated, water vapor will not penetrate to any extent. On the untreated backside, the water vapor will penetrate and the wood will swell. This uneven absorption will cause one surface of the wood to swell and not the other. The individual boards will then cup towards the finished surface.

Cedar and Pine are very porous and soft materials. Unsurfaced, they will absorb any airborne odors (body, cooking etc), water moisture which will allow expansion and contraction, and the surface will be susceptible to abrasion and splintering. They will also be susceptible to stains and dirt. The Cedar, especially, will constantly give off an odor, which if you are sensitive to allergies, can be an irritant. An oil based polyurethane satin varnish, will result in a very pleasant finish, that's both durable and good looking. It will take three coats to completely seal, and fill to smooth, the front surface of the Cedar. You will have to sand after the first coating, before the second and third coatings are applied. Pine can usually be surfaced with two varnish applications for a satin finish.

Most pre made tongue and grove Cedar boards are only available in 1 x 6 widths. Some speciality yards can get 1 x 4" widths which would work well in curved wall or ceiling applications. If you have a router and a table with a fence, you can fabricate your own tonge and grove boards, of any width as necessary.

My original estimation of the cost of a DR interior did not include the cost of Cedar materials. It including the pricing of pre made 4' x 8' paneling. This project could easily double my original estimate.

BOL  Gard

I did my own, using the tongue & groove paneling. I used finished nails to secure the wood to the strips and it's worked out great. I'm about 80% finished (hot Tx summer slowed me down), but I've used it a lot and it's held up well....

Mine is a 4' SW with shower, sink, fridge, cabinets, etc. The paneling is one of my favorite features. I just need to get off my duff and finish it before next year.

4' SW, slant not straight.

It's cramped a little, but it serves all my purposes and I utilized all the space I could.

Probably so.

My short wall is 4' long. My long wall is 8' long. There's diagrams in my album.

http://www.horsetrailerworld.com/forum/photos/show-album.asp?albumid=138&currentpos=1

If you want to get an idea of what will fit into a small space, look at the want add photos in HTW. A four foot slant wall LQ is commonly called a "weekender". It can easily include a bathroom with a separate shower, kitchenette, cook top, fridge, microwave, hot water heater, storage cabinets, heater, water tank, air etc.

It will easily be comfortable for a couple of people for a couple of days.

Gard