@Jeremy Paschedag
@John Leavelle seems to have covered the rough numbers for the cash out refinance pretty well and I am not expert in that matter so I don't have much to add to that.
However, you asked about the HELOC. I recently looked into HELOC in Texas (the rules are different in other states) and it seems like banks will only do the HELOC on your primary residence (maybe I didn't look hard enough). There are small closing costs (a few hundreds typically) but the interest rate is variable. Some may have a yearly fee (usually around $100 or so).
The bank will use the same criteria (approx. 80% LTV - money still owed) to determine the max amount for the line of credit.
You may be able to find a HELOC with interest only for the "draw period" (which I have typically seen at 10 years but it could be different) but most of the ones I looked at required interest + principle payments. During the draw period, you can draw as much money as you want (up to your HELOC limit) whenever you want. After 10 years, you cannot draw money anymore and you have 20 years (again, typical of what I have seen but could be different) to repay whatever you still had taken out by the 10 year mark (still with a variable rate).
The benefit of the HELOC is that you do not have to take any money out when you open it. So you only start paying interest when you take the money out, which could be 6 months down the road. You can use that money for the down payment of another house or to pay it in full and then refinance the house after a year, put the money back in the HELOC to avoid paying interest and take it out again when you need it. Please keep in mind that you may have prepayment penalty in your state.
One of the main problem is that the interest rate is variable, so you really don't want to be in a position where you have to keep the money out very long as the rate could climb up.
The other problem I have heard of but haven't had time to investigate further is that, apparently, the bank can call the HELOC at any time, meaning they may ask you to reimburse all the money they gave you at one point if they feel like it. So you would have to cover that risk by having a plan to get that money if that was ever the case.
People seem to have better luck getting better terms with small credit unions. I did not in my area so far.
Hope this helps!