I didn't have a financial dilemma when I built my layout in 2008, but I am frugal so I set out to get bench building materials at the least cost.
Home Depot gets many lumber products on banded wood skids, and they throwaway the skid lumber. Go to the department manager and ask for the lumber free of charge.
Home Depot also sells remnant pieces of lumber for 50 cents apiece.
Home Depot sells Oops Paint for 50 cents a jar. Collect shades of green, brown, red and yellow.
Lowes sells a gallon of white glue for $10. My layout is 60 feet of 3 foot wide benches and it has consumed 1.5 gallons of white glue so far.
Appliance box cardboard is ideal for sound deadening the bench top, and construction projects. The good news is this cardboard is usually free at appliance stores and at the curb on rubbish collection day. Collect the cardboard with one and two layers of corrugations. The two-layer stuff is typically 1/8" thick.
Keep cereal boxes as they make good skeletons for card-stock buildings.
Card-stock building kits are available from Gary Johnson and others and they usually cost $10 or less. Gary posts his kits on eBay, Search for "Card buildings." Gary's address is PO Box 157, Mt. Dora, Florida 32756-0157.
Card-stock is free from file folders and cereal boxes. A package of colored paper from a dollar store is useful for building structure roofs.
Dollar stores have lots of useful layout scenery tools such as squirt bottles, spatulas, measuring cups, plastic storage bags, etc.
Saw dust is an excellent ground cover material and it's free at middle and high schools with industrial arts curriculum. Sprinkle the saw dust into place, shape it, and secure it with a mixture of white glue, water and Oops latex paint.
Wood coffee stirrers cost me $2 per box of 1000 at a local deli. There have been many coffee stirrer projects posted on this forum. Do a search.
Here's a link to a model railroader who makes trees from low cost common materials.
http://www.youtube.com/watch?v...&feature=related
Network with some folks in the building trades to some wire. An elevator mechanic gave me bundles of wire being scrapped from elevator maintenance projects.
If you have the will to build it, you will find the ways and means to make an affordable layout. There are many on this forum who will guide you, so get started.