£30 a month sounds about right to be fair but I'm sure you could get it cheaper if you moved to Scottish Hydro's Price Fix 2008 product.
The reason you owe £94.77 is that the provider has underestimated your consumption and therefore your DD of £30 has not covered it. Providers normally review DD payment every 6-months and so during that time you have built up a level of debt which needs to be paid off.
One way to avoid this is to sign up to an 'Online' tariff and ensure you are providing "actual" meter readings rather than allowing your provider to "estimate" them.
Online tariffs include:
British Gas - Click Energy 4
Scottish & Southern - Price Fix 2008
Npower - SOL8
Powergen - Energy Online Extra Saver 3
Scottish Power - Online Energy Saver 4
EDF - v5.1
There are two types of tariff that a provider may offer - Standing Charge and No Standing Charge.
Standing Charge - is a fixed daily charge that will be paid each and everyday regardless of whether any energy is used. There is then a set unit rate charge that applies to each unit of energy consumed. The fixed standing charge will be circa 14p per/day with the actual unit rate being circa 9p per/kwh.
No Standing Charge - these tariffs (as stated above) have a 1st and 2nd Tier unit rate with no standing charge. The 1st Tier rate will apply to the first set amount of energy used i.e. for electric it is normally the first 900kwh of use per annum. The 2nd Tier unit rate will be less than the first and will be charged for the remaining units used.
Use the comparison tool at the top of the page ('Gas & Electricity'), enter your postcode and compare your current deal with the best on the market to see how much you could save.
Hope this helps.