The checkout process should not interfere with how you are adding the items to the cart with options. Do you still get the correct result for the items and their options when you are adding them to the cart? If so then you should be fine to just create a new set of checkout pages. In the last step of the wizard you can name the pages however you would like to keep them unique.
I would strongly suggest against using Payments Standard, I find it much more difficult to work with and implement, and you will not be able to know the status of a transaction when the user is returned to your site. If you use Payments Standard you will need to rely on an IPN page to gather the info that PayPal posts back after the transaction occurs.
If you are concerned with the monthly cost I would suggest that you use Express Checkout only as the payment option. This should give a very similar experience to the user that goes off to PayPal to login and approve the transaction. The biggest difference is that the user will be returned to your site and you will know the status of the transaction when it occurs rather than waiting for a notification being sent to your IPN page.