You certainly understand the situation your in. I'm happy to see that you have also read the rifle reviews.
Althought the S410 would be an excellent buy you have then to consider how to re-charge the rifle. My recomendation would be to do it yourself with a spring powered rifle using open sights at ranges of 20-25 yards. Practice on paper targets until you can group your shots inside a 1 1/2 inch circle.
The rifle that won't break the bank but gives full power (UK) and good build would be the Cometa Fenix 400.
Youngmans Sporting Guns
19 / 20 Market Row