1bn a year is peanuts compared to the potential downside
Britain's annual GBP = GBP453 billion (Q1 2016 estimate)
1bn = 0.2% of GDP
Annual GDP growth forecast = was 2.1%, recently downgraded to 0.4% following Brexit
So that's around 8 year's worth of net benefits lost already.

Debt repayment is more interesting. Current national debt = around GBP1.6 trillion. Annual cost to service debt = GBP43 billion.
1bn = 2.3% of 43bn.
So a tiny change in the interest rate will affect debt repayments far more than then scale of potential net benefits from reduced EU payments. And interest rates depend on credit ratings, and exchange rates...
(Smale is stuffed, Wed 29 Jun 2016, 14:23, 1 reply)

sure, but that's the impact of Brexit itself, not Britain's economy outside the EU
Uk's exports to the EU dropped by 7% last year, and have grown by a meagre 3.6% over the past 15 years, compared to double that for non-EU exports. So the freedom to trade with non-EU countries on its own terms rather than the bloc's makes more sense for the economic future.

As for interest rates; they've been fucked for a long time either way. They can't stay at or near zero forever.
( Grrrmachine the indifference engine, Wed 29 Jun 2016, 14:40, closed)