I’m not exactly sure what it is you’re trying to do really.
You’re looking for posts that do not have any value set for “status” and a value in “sale_price” that is < 300000?
If this is correct then:
'meta_query' => array(
'relation' => 'AND',
array(
'key' => 'sale_price',
'value' => 300000,
'type' => 'NUMERIC',
'compare' => '<'
),
array(
'relation' => 'OR',
array(
'key' => 'status',
'compare' => 'NOT EXISTS'
),
array(
'key' => 'status',
'value' => '',
'compare' => '='
)
)
)