Leach is entering his tenth year in the league, and will turn 32 near the beginning of November. If he signs a Minimum Salary Benefit (MSB) contract, he stands to make a veteran minimum of $840K in salary for players with 7 to 9 years worth of accrued seasons (Leach has 9).
Source: http://www.steelersdepot.com/2011/07/2011-2014-nfl-minimum-base-salaries/
In addition to that minimum base salary (paragraph 5 money), Leach would probably get a $65 K signing bonus, which is what the Giants have done with their 11 MSB players--the most in the league. He could potentially stand to make a salary of $905 K, with a $65 K bonus included, and only count $620 K against the salary cap. You wouldn't subtract that $620 K cap figure from a given team's cap though if he signs. You would subtract the difference between Leach's hypothetical $620 K cap number from that of the 51st ranked cap figure on the team, which in many cases is somewhere between $480 K and $555 K. If we take the low number, than the displacement differential would only be $140 K. Subtracting only $140 K from a team's cap number for a player like Leach is a no-brainer, particularly if there is a glaring need on the roster for a Fullback. There is no question that he should be able to find a job in the league under those circumstances.
His agent's job is to look for team's with openings on their rosters, whether through dearth of talent, lack of depth, or otherwise. It would also help if those teams have some cap room, so his agent could negotiate some extra dough for him. Odds are though that he'll probably wind up getting the MSB I mentioned above, unless he gets a team with salary cap room, like the Dolphins, to fork up some dough (he would reportedly prefer to return to Houston, but the money might not be right). Here are two good articles on the topic, one from Miami and the other from Houston:
http://www.miamiherald.com/2013/06/13/3448179/miami-dolphins-trying-to-lure.html
http://blog.chron.com/ultimatetexans/2013/06/vonta-leach-still-in-miami-agent-cites-mutual-interest-with-texans/
It'll be interesting to see what happens, but either way I'd consider it highly doubtful that he signs with the Giants, for two reasons:
1. Leach is NOT a stop gap type of FB; he's arguable the best blocking FB in all of football, hence there would be more of a demand for him, than that of the Tony Fiammettas and Evan Rodriguezs of the league.
2. Even if Leach winds up signing a MSB contract, he will want to go somewhere where he can showcase himself for 2014 when he re-enters the FA market. Leach can only do that if he is the undisputed starter on a team WITHOUT someone looking over his shoulder, ready to take his job from him. He can't do that on a team like the Giants where the starter is expected to return early in the season after missing a few weeks at the start.
Besides those two reasons, teams don't usually care more than 1 FB in today's NFL. I would have loved Leach on the Giants if Hynoski wasn't here, but that ship sailed already (they tried to sign Leach to an offer sheet before the 2007 season). My money is on either the Dolphins, or the Texans. Going back to the Ravens makes little to no sense for Leach, especially because Baltimore drafted his replacement this past April in the 4th round, in the person Kyle Juszczyk out of Harvard.