Substitute Dumb Bells with food tins from the cupboard.
Start with small tins and gradually build up to larger heavier ones.

TIP:- Wrap some elastic bands around the tin to improve grip.

For a slightly heavier weight, substitute a kettle bell using a plastic Milk or Juice container.
This can be filled up to match the weight you desire.
(1pt of water =approx 1LB).

TIP:- Wrap handle with piece of foam pipe lagging and then tape or glue into place to reduce rubbing and prevent blisters.

Expensive exercise steps can be replaced by using a sturdy heavy and stable box or wooden block.

Better still just use the lower steps or your staircase, this has the advantage of having a grab rail for initial support.

Camping mats tend to be far cheaper than those sold specifically for exercise.
Look in the supermarkets such as Aldi or Lidl, they often sell cheap.

Exercise balls are a great tool to use, Argos sells them very cheap (£8 - £10) and in two sizes.
Remember you need a bicycle pump and adapter!