You can increase the price of a plan using a negative promotion. So for example a promotion with -50 increases the price by $50. You can then have the promotions configured to apply if XYZ field option is selected. Currently that's the only way to do what you're wanting beyond having multiple plans with different prices that are conditioned to display based off option selection. Another alternative is to use a parent plan with the options being child plans of the parent, but you'll run into issues with renewals since you can't renew multiple plans at once.