1. As a general rule it is cheaper to make up you're own food mix.

 

2. If you are making up you're own food mix, buy the larger bags of home brand bird seed.  There is not much variation in the quality of seeds, a lot of the time they have come ffrom the same farm as the more exspensive brands. 

 

3. Visit your independent pet shop.  While there are some reasonable pet shop franchise chains out there, they are generally slightly more expensive.

 

4. Visit an orchard (if possible) for your fruit such as apples.  Many orchards sell juicing apples extremely cheaply due to marks on the skin or the odd bruise, which can simply be cut off.  Also keep a look out for horse carrots, they are the strangely shaped or split carrots that some greengrocers sell cheaply.

 

5. Start collecting carrot peels, celery/carrot tops and apple peels/cores.  Your rat won't mind that they are the off cuts and they are just as edible as the rest of the vegetable.