If I want to buy BTC with PayPal, so I buy SLL, then use the SLL to buy BTC, how much money would I lose in the process?
~15% to 20%.
If you have cash and are looking to buy at least $50 worth it may be cheaper to buy it using GreenDot MoneyPak (flat $4.95 fee).
Since MoneyPak has a flat fee the larger the purchase the lower the %.
$50 MoneyPak = 10% overhead
$100 MoneyPak = 5% overhead
$250 MoneyPak = 2% overhead
$500 MoneyPak = 1% overhead
I'll trade you (at MtGox last price) even without rep under the following conditions:
a) you send code first
b) you purchase with cash only (it will reflect on receipt if you use a debit card)
c) you write on the receipt my name (PM me for details)
b) you email a scan or photo of the receipt when you send the code.
You can have your coins in minutes at a much lower markup than SLL.