Scotland receives money from the UK in roughly the same proportion that the UK borrows money from gilt investors. Scotland would certainly have a budget deficit after independence, but not out of proportion with its size.
What interest rate they would have to pay on that debt is a different question...
Scotland receives money from the UK government in the form of a block grant. Scottish companies and residents also pay taxes to the UK government. At this point in time, Scotland contributes more in taxes than it receives through the block grant.
The basic facts are that Scotland accounts for 8.4% of the UK population, 8.3% of the UK's total output and 8.3% of the UK's non-oil tax revenues - but 9.2% of total UK public spending.
In other words, "if you ignore one of Scotland's major economic outputs."
What interest rate they would have to pay on that debt is a different question...