I think this is the best approach.

Given that いちば is always a physical market, and しじょう is usually "market" in the abstract sense, I think it's best to keep the entries separate and add a new sense here that points to いちば.
Probably don't need an econ tag if we go with this approach.

@@ -18,2 +18 @@
-<field>&econ;</field>
-<gloss>market</gloss>
+<gloss>market (financial, stock, domestic, etc.)</gloss>
@@ -22,0 +22,7 @@
+<sense>
+<pos>&n;</pos>
+<xref type="see" seq="1308300">市場・いちば・1</xref>
+<xref type="see" seq="1308300">市場・いちば</xref>
+<s_inf>usu. read いちば</s_inf>
+<gloss>(street) market</gloss>
+</sense>

I could live with a single entry provided it was clear that things like "futures market" 
were usually しじょう. I feel that two senses is the way to handle it. The JEs have two 
entries, with fairly distinct glosses.

any thoughts about merging this with いちば with a note?

at a minimum, i suggest copying the news tags in from there because it's quite likely that this entry is the source of most of those hits

@@ -6,0 +7,2 @@
+<ke_pri>news1</ke_pri>
+<ke_pri>nf01</ke_pri>
@@ -10,0 +13,2 @@
+<re_pri>news1</re_pri>
+<re_pri>nf01</re_pri>

otoh, maybe not.  temp approve because i've just changed いちば so it is virtually identical with this entry

@@ -15 +15 @@
-<gloss>(the) market</gloss>
+<gloss>market</gloss>
@@ -16,0 +17 @@
+<gloss>exchange</gloss>