Making a terrarium is easy and cheaper than you think.  Each plant 2.95 at a home improvement store, rocks 1.00 at a dollar store and glass easy to find at a thrift store.

Plant your plants

Online instructions say you need cactus soil, but cactus soil is just like potting soil with extra sand.  I had potting soil, and play sand, so I mixed to too to get a good consistency.  Succulents need lots of drainage so add rocks to the bottom of your glass.  I found pebbles at a dollar store for a dollar a bag and I used 1.5 bags.    One bag for the bottom, and less than that for the top to give it a finished look.

Add Gravel

I ended up making two.  The second one cost me a grand total of $13.  $2.00 for the rectangular vase from a thrift store, $9.00 worth of plants, and $2.00 of rocks.  I had the sand and potting soil already.

Side View

Looking from above