There becomes a point of diminishing returns on cables. While the included cables may be of good quality if you specified, or negoitated them, standard "throw in's" have poor construction, bad connectors with poor contact area materials. It is easier to "hear" poor cables in an excellent system, than excellent cables in a poor system.
If I remember the equipment you had on your list, you should not subject it to throw in cables. But you need to determine what you have been given. I would not go overboard, but you should be able to get suitable quality for less than $100 for interconnects for electronic equipment. Speaker cable is of the same mindset, but prices are dependant on the length you require.
Here are numbers I have seen advertised (this is not a recommendation, but a point of reference)
- Monster Cable Interconnects ($50-75 per metre - gold plated connectors)
- heavy gauge speaker cable (12g $1.50 metre)
- speaker connectors (gold plated $15 per 4 - you will need 8)