just a thought next time you get to a beach its amazing what usefull bits you find on the strandline
I use drift wood odd plastic containers for scenery projects
barnacle shells make interesting additions to bases the larger sizes in clumps make stange plant forms as does the calsified cases of marine worms usually attached to small rocks
living in cornwall I have beaches in easy reach our sand contains quartz (glitter on a base) bits of shell ect and you can even grade your sand for bases on the particle size depending on where you collect it from as a tight ase i keep my eye out for all kinds of free stuff for modeliing
foamboard ask your supermarket many of the promotion signs are made of it and they only dump them same with good quality card signs
my local recycling centre is a happy hunting ground for old tv radios ect for bits
I am much inspired by the terragenasis site (spelt wrong?) as a newbe I have been much impressed with the modeling skills of everybody
keep it up