According to “man 5 crontab” you can set environment variables in your crontab, by writing them before your cron lines.
There is also an example of a crontab so you just have to copy/paste it :
$ man 5 crontab | grep -C5 PATH | tail
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# m h dom mon dow usercommand
17 * * * * root cd / && run-parts --report /etc/cron.hourly
25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
So you can adjust your PATH or any environment variable to whatever you want. But this example seems enough for typical cases.