Sorry to say but the Metro doesn't count for a MPA type rating. Ref JAR-FCl Section 1 Appendix to JAR-FCL 1.220 (page 90).
The cheapest MPA is a Shorts 330/360 conversion. That's what I did but I don't really recommend it. It took ~6 months or so with a lot of running around to get it done. I ended up paying £10,000 plus CAA fees for it. You may be better off looking at the ATR, Dash 8 or the 737/A320 type rating to do the conversion. You'll need to read the
TRTO list