With that budget, you're looking at a mid to upper grade indoor system. The condenser is fairly new, so you could pair it with a 13 SEER coil provided you use a TXV (make certain the coil has this--thermal expansion valve). The problem is you don't know the exact capacity/efficiency with a mismatched system, and the warranty may be subject to void. It's not as easy as just installing a bigger system. Your duct system likely can't handle a 1 ton increase in airflow, so not only will you not get the nominal capacity delivered, but you could run into noise from going up a ton in size. A heat load calculation is used to determine your sizing. Why increase? Oversized systems are inefficient and tend to not last as long (if very oversized). For the indoor unit, I would recommend an AFUE of 90% (furnace efficiency) if PVC venting isn't an issue. A variable-speed blower would be nice, but not needed to have a good system (helps with dehumidification and efficiency). You really should have matched the coil in the first place to avoid this predicament, but hind sight is always 20/20. Also, the company who recommended the partial replacement may have screwed you over.

Thanks Ryan, sounds like staying with 2-ton it better and I will make sure it has the TEV. The partial replacement was my idea, because I can't afford to get a new condensor right now. If I buy a new condensor now then I'd have to sacrifice to fit budget by getting lower quality units for the coil, air handler, and furnace. Is 13 SEER the best I can use for this coil setup, given the 10 SEER condenser, or can I look into 15 SEER or 19 SEER for the coil?

The SEER is determined primarily by the condenser unit which you have now, 10 SEER. The larger 13 SEER coil (new indoor coils don't really have a SEER rating, but I'll call it 13 SEER anyway) may or may not increase your efficiency by a small amount. The TXV will help with refrigerant metering. I don't have a huge problem with mismatched coils on straight A/C systems as long as the coil is larger and has a TXV. A heat pump would be a different story. It would be more of an issue if the coil were older and you replaced the outdoor unit. Coils are upsized all the time to get higher efficiency. However, they are still technically "matched" and rated, so you know what you're getting. Some manufacturers/distributors will void your warranty if you have a mismatch. To answer your question, you don't have to worry about SEER since you're stuck with the 10 SEER outside. If you get a variable-speed motor, along with the slightly larger coil, it may bring your efficiency up a small amount. Can't know with a mismatch since it's not in the AHRI ratings database.

Good info, thanks! Another reason I'm concerned with SEER on the inside components is for future improvements. So if I buy a 19 SEER condenser in a few years, it will work OK with the interior parts that I buy today. Is the coil itself pretty much the same for the different efficiency models (just larger size)? I guess the furnace air handler is the other important part. If I get a variable speed fan (that can do higher SEER for the future) I would just have it locked to single speed so that the coil does not freeze up with the single speed condenser that I currently have?

I don't see why the coil would freeze due to you having a 10 SEER condenser. If anything, I'd think the coil would run a little warm to begin with, though the TXV would help. Indoor coils are rated with multiple different SEER outdoor units.