A 20% or higher borrowing fee is quite unusual, and would only be for very hard-to-borrow stocks that most brokers wouldn't allow you to short at all. With IB you can short almost anything (currently 8025 US stocks) but it might be expensive. You can see the current fee and 10-day history under Account Management -> Tools -> Short Stock Availability. For easy-to-borrow stocks like MSFT or CAT the borrowing rate varies from 0 to 0.12%. annually.
On the other hand, if you want to short Citigroup (C), you can do it but the borrowing fee is 108% right now, because you have to outbid all of the other would-be short sellers. I'd never pay that much, but if you're an expert in the stock and you're sure it's going down fast, you might be willing to pay that for the privilege of shorting it.
I believe that you only pay the borrowing fee if you hold overnight; I don't think you pay if you day-trade.
In more normal times IB pays you interest on short sale proceeds; right now the rate is 0%, but someday rates will rise which will help offset any borrowing fee or even pay you to hold a short position.
I don't have any problem with how IB handles this, with the exception that I'd like to see the borrowing fees itemized by position in their reports.