If you just want to find out if your upto Class 1 eyesight before committing to the £400, then a visit to your local optician with a copy of the Class 1 requirements should do.
I visited 'Specsavers' and got the full test - colour, refraction, fields, accomodation, acuity etc. - for just £15 including the report.
Just send that off to the CAA and they should tell you if any problems are likely.
You'll still have to go through it all again though when you do the initial Class 1.