I'm having a hard time trying to price my combos, does this sound like a good plan?

I'm in the process of developing nine different combos of my software and web-based services for selling on eBay specifically, but deciding on prices is harder than I thought.

I sell both a basic and standard software and sell the web based service by month. I will sell a total of 9 combinations:

3 Months
6 Months
12 Months

Basic + 3 Months
Basic + 6 Months
Basic + 12 Months

Standard + 3 Months
Standard + 6 Months
Standard + 12 Months

My main criteria is that I want the Basic + 3 Months to be about $8-10 and want the Standard + 12 Months to be around $30-50.

So far the best thing I could come up with using an excel sheet where I enter the prices for "basic", "standard", and for each 3, 6 and 12 months and then it adds them up, (is this a good way of deciding on prices for combos?) is to give the basic version for free with the purchase of online use, sell the standard version for $12, and sell 3, 6 and 12 months for $8, $15 and $25 respectively.

I realize this makes the strange situation where buying the web based service alone costs the same as the same amount of web based service with the basic edition, but this would allow me to include "+ FREE software" in my title for those listings.

Do you think this is a good pricing plan? The end result being:

3 Months $8.00
6 Months $15.00
12 Months $25.00

Basic + 3 Months $8.00
Basic + 6 Months $15.00
Basic + 12 Months $25.00

Standard + 3 Months $20.00
Standard + 6 Months $27.00
Standard + 12 Months $37.00

So does this sound good or should I make any changes? The prices are cheaper than on my website to compete on eBay.

Thanks