42/7=6x.The classic answer then is an alpha 1.5-6x. Your budget doesn't really fit that, though. There's the Burris MTAC, but I haven't tested it to know if it'll do.
You may find as you get older that a more upright head position gives clearer vision; particularly with glasses. A medium mount can often handle a larger objective. That opens some possibilities for closeout priced scopes which have larger than 42mm objectives.
