Well, if you were to get an unsecured personal loan, CC cash advance or 2nd lien HELOC, you would be looking at much higher rates than a traditional mortgage anyway. You also mentioned you wanted to use the money to start a business, if you already have something going on that front, you can look into a SBA loan. Given what you said, you don't have a lot of options.

Banks don't like to take 2nd lien on a property these days, which is why they are offering you a much smaller line than what you have in equity. You can either try asking your existing mortgage lender for a line - they would be more open to it since they own your first lien too - or look into a cash out refinancing. That's getting a new mortgage with a higher amount than what you currently owe and you can take the extra cash.

Higher returns come with higher risks. Do you really understand the risks? Also short-term capital gains (realized within 1 year) are taxed higher than long-term gains in the US.