A bipartisan Senate group has agreed on a sweeping legislative proposal that would represent the most ambitious overhaul of the U.S. immigration system in three decades. The Washington Post will be examining portions of the bill on Post Politics in a series of blog entries.

How much should a person who's been living in the country illegally have to pay in penalties to get right with the law?

That was one of the innumerable tricky issues that faced the Senate's immigration Gang of Eight as it negotiated an immigration overhaul that will be introduced this week. As with most issues in the complex debate, it required a careful balance.

Many Republicans sought a serious fine, something that would ensure people paid a real price for having broken the law.

But many Democrats and immigrant advocates wanted to make sure the penalty was not so high that immigrants, many of them working low-wage jobs, would find it impossible to pay. They said an estimated $9,000 in penalties was one reason a similar bill failed in 2007. They reasoned that if people couldn't pay the penalty, they might choose to skip it and remain in illegal status — undermining the whole point of the legislation.

According to a summary of the bill, here's where the gang came out: Those now in the country illegally would be required to pay an initial $500 fine to achieve a provisional legal status. They would also have to pay "assessed taxes" and "applicable fees" to cover the cost of processing the application, but the summary of the legislation, set to be introduced later Monday, does not provide further details.

After six years in provisional status, immigrants could renew their authorization, but only if they paid another  $500 fine. When they sought permanent residency — estimated to occur in about a decade — they would pay a final $1,000 fine. As a result, they would over time pay a total of $2,000 in fines, in addition to other processing fees.

Frank Sharry, executive director of the group America's Voice, which supports the overhaul, said he's been told that the fines were one of the most difficult issues to negotiate and have been adjusted even in the final days of the negotiations. "It's been a moving target," he said.

He said the fines included in the bill summary are "more reasonable" from his perspective than the higher numbers included in the 2007 effort. But he said many questions remain to be answered. They include whether every member of a family seeking provisional status would be assessed the same penalties or if the penalty would be assessed once per family. It also unclear how much applicants would be required to pay in back taxes and how high additional processing fees are likely to be. "The details matter," he said.