Free or inexpensive VCS with "Lock" instead of "Merge"?

I'v开发者_C百科e been using several VCS systems and wondered:

Is there any free or inexpensive VCS with ability to lock files instead of constantly merging?

Almost all the open-source VCSs out there support merge... but if you generate 1 too many revisions, there is too much to merge and after while, source code goes crazy trying to deal with all the merges.

Problem: We have a team that generates ~ 100+ changes per day and merging a team of changes leaves us swamped with many, many changes each developer has to commit.

Any ideas for a better solution than merge?

Using HG (Tried GIT, Bazaar, etc.)

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SVN allows you to lock individual files. There's no support for locking whole directories though.

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SourceGear has a free source control product as long as it's only used by 1 developer.

www.sourcegear.com