HELOC max LTV's range greatly and oftentimes are determined by property values, credit score and risk tolerance of lender. Where I work we go up to 95% LTV on HELOC's but we also raise the rate a few points once you go over 80% and again over 90%.
Most companies are either going to charge a closing fee(application fee), annual fee, or sometimes both. Oftentimes the 1st year annual fee will be waived, and sometimes banks will do promotions and waive these fee's.
Since most places portfolio their 2nd mortgages the underwriting criteria will be different as well. Depending on your income situation your DTI could be affected by the total unused balance of a HELOC..so if the magic rate you're quoted as a minimum line amount of say 50 or 100k be aware that could impact your borrowing power in the future(i'd ask ahead of time how they treat this!).
Double check you are allowed to purchase real estate with your HELOC or fixed 2nd as some places bar this practice.
If you were planning on paying this loan back over 2-3 years you'd probably be best doing a HELOC(remember most are interest only so no principal paydown on regular payment), after that it's a major toss up based on current rate environment compared to what it COULD be.
