Eastward Ho! To the Editor: Why Paul Eldrenkamp does his own books ("Why I Keep My Own Books," 1/92) is not the same reason I do. My main reason is that I can do them cheaper than my $50-per-hour accountant since I get $30 per hour for my time ($25 per hour for my carpenters). If, as Mr. Eldrenkamp suggests, he is charging to meet his target of $40 gross profit per hour and his costs are $25 per hour, then he must be charging $65 per hour. The likely effect of Eldrenkamp's article will be less the encouragement to bookkeeping and more to the mass-migration of southern and midwestern construction people out here, where rumor has it a man can make $65