SQL запроса:

SELECT   wp67_posts.*
					 FROM wp67_posts  INNER JOIN wp67_postmeta ON ( wp67_posts.ID = wp67_postmeta.post_id )
					 WHERE 1=1  AND ( 
  wp67_postmeta.meta_key = 'average_price_week'
) AND wp67_posts.post_type = 'boats' AND ((wp67_posts.post_status = 'publish'))
					 GROUP BY wp67_posts.ID
					 ORDER BY wp67_postmeta.meta_value+0 DESC
					 

Первые 20 постов и meta:

ID: 1208 — title: Kaja — meta: ['16900']
ID: 1207 — title: Dali — meta: ['5580']
ID: 1206 — title: GILLEPSIE — meta: ['5920']
ID: 1205 — title: Odisey — meta: ['4800']
ID: 1204 — title: Mareta — meta: ['4800']
ID: 1203 — title: Altea — meta: ['4080']
ID: 1202 — title: Sunsailor — meta: ['3080']
ID: 1201 — title: Flash — meta: ['2760']
ID: 1200 — title: Art Vandelay — meta: ['4912.3076923077']
ID: 1199 — title: KRISTINA — meta: ['1480']
ID: 1198 — title: Magic — meta: ['1300']
ID: 1197 — title: Teo — meta: ['1180']
ID: 1196 — title: SANDOKAN — meta: ['1180']
ID: 1195 — title: Zaurak — meta: ['8790']
ID: 1194 — title: Helix — meta: ['1260']
ID: 1193 — title: Salona 45 Performance — meta: ['4338.6']
ID: 1192 — title: Salona — meta: ['2812.8']
ID: 1191 — title: Sandro — meta: ['1600']
ID: 1190 — title: Sandy — meta: ['6100']
ID: 1189 — title: Storm — meta: ['5520']