You asked for simple, and I promise you this is... it just looks a bit math-heavy to start with because we have to handle a couple of different scenarios. Bear with me :)
I find the best way to deal with these kinds of questions is to put together a "Total cost" for each option, for a sensible amount of time, and see what the difference is. We'll include the current cost for both options, plus the subsequent costs for 12 months: I find that more useful than a straight "which is more expensive right now" because it includes the potential costs of the next upgrade, and any changes to the plan.
Let's throw some numbers together for the next 12 months (if your current plan is longer than 12 months, read the note at the bottom first)
First, write down the cost of these things
- m = number of months left on current contract
- a = monthly cost of current plan
- b = monthly cost of upgraded plan (if you upgraded with the same company)
- c = monthly cost of a new plan (the plan you'd choose if you didn't have to upgrade with the same company**)
- Pu = upgrade cost of current plan (the up front fee, not the monthly)
- Py = new phone cost (assuming you weren't intending to upgrade but were going to buy a new phone**)
- Pe = how much the current phone (if in working condition) would sell for on eBay
**The above assume that you have two options if you take the repair option (and only one option if you use the buy-out option). The two options we're assuming here are that you can either:
- Upgrade the current plan with a new monthly (b) and initial cost (Pu)
- An entirely new plan with a different new monthly (c) and initial cost (Py)
If you'd choose the same new plan regardless of whether you take the $100 or $150 option, there's no need to include both options: to simplify things you can just use the same numbers for both b/c and Pu/Py and the calculation below will still work.
When you've found and written down the above, just do the sums below to find your two total costs over 12 months. Nothing fancy, just plug the numbers above into the equation. eg if Pe (eBay value of the phone) is $80, replace Pe with 80. Don't forget to do the parts in brackets first!
- Option 1: Repair the current phone, then sell it on eBay when you upgrade/switch plan later as normal
- 150 - Pe + (m * a) + ((12 - m) * c) + Pu
- Explained: 150 you'd pay now to replace the phone, minus the ebay cost (minus because you get it back), plus the rest of the current plan, plus the new plan for the rest of the year, plus the cost of upgrading at the end of your plan
- *Note that if you just want to keep the current phone once it's been replaced, and get a new plan, you can take both -Pe and +Pu out of this equation!
- Option 2 Buy out your current contract and upgrade immediately
- 100 + (12 * b) + Py
- Explained: 100 to buy out your contract, plus 12 months of the new contract, plus the cost of a new phone
That's your total cost for both options for the next year.
Note: I'm assuming that your plan ends within the next 12 months. If not, just replace 12 in the above calculations with another term! You can also do this if you want to find out the price difference over a longer period (noting that if you upgrade to the same plan regardless of choice, you'll get the same answer for any period longer than your current contract)