I rent two huge O2 tanks for $12/month each to refill my much
smaller flight bottle.. while I never get 3,000psi on refills
I can do ~10+ refills above 1,500psi before I refill the
lower stage tank.

but here is a pump and O2 concentrator that can top your tanks
to 1,500psi (half full) every day... at $3,000 (real world) its
an impressive two stage 15psi input pump for that price..

http://www.invacare.ca/cgi-bin/imcanada/inv_catalog/prod_cat_detail.jsp?oidOfProduct=536926953