3 Options Brokers of interest, cost comparison: TOS, TastyWorks, IB


Commissions and margin costs are a significant factor, as is technology and ease of use.
Regarding the costs, can someone tell me how much the brokers TOS, Tasty Works and IB would charge for an account with a net liquidation of 5000USD, and short 100 SPY at $225, per annum?

:?:For TOS, https://www.tdameritrade.com/pricing/margin-and-interest-rates.page

it seems the cost l would be charged 8.25%+1% = 9.25% x (22,500 - 5000) = $1,618 annual margin cost, correct?

:?:For Tasty Works, https://tastyworks.com/commissions-and-fees.html
it seems the cost l would be charged 8.00%+1% = 9.00% x (22,500 - 5000) = $1575 annual margin cost, correct?

:?:For IB , https://www.interactivebrokers.com.hk/en/index.php?f=1595, it seems the cost l would be charged 2.66% x (22,500 - 5000) = $465.5 annual margin cost,
are the numbers correct?

:?:in conclusion, TOS, TastyWorks both charge ~4x more than IB?

:?:Also if held short SPY for the year, I would be expected to pay 4 dividends on top of that right?

:?: Lastly, l have ~$50K to deposit in one of those brokers, it seems only IB gives the highest % on deposits, +0.66% for deposits >10K USD, and offers 5.821% on ZAR, South African currency. Anyone have any ideas why the interest rate offered for ZAR is substantially higher? as l am seriously considering buying ZAR with the portion of the cash not used for trading. Thanks in advance for advise and views ;)